Massive COVID-19 Testing: 30 Million Tests/Week

Population COVID-19 testing

Population-wide testing to identify symptomatic and asymptomatic infections could be a powerful tool to control Coronvirus Disease 2019 (COVID-19) spread, but current global testing capacity does not permit widespread testing of asymptomatic individuals. These tests are still limited to individuals who are symptomatic with limited availability to those with recent exposure to an infected person.

Because of the high prevalence of asymptomatic COVID-19 infections, proposals from the Rockefeller Foundation for disease mitigation include widespread and frequent testing of the US population. In the United States, diagnostic testing for SARS-CoV-2, the causative virus of COVID-19 is currently >2 million per week. Estimates for US testing needs for population wide surveillance range from 30 to 300 million per week. In order to scale testing by an order of magnitude, novel technologies and rethinking current testing paradigms are needed. The NIH has initiated a rapid funding program to develop SARS-CoV-2 testing, and these new technologies may play a part. However, we can broadly conceptualize key problems to address in population-wide testing in the US. The first is high-sensitivity testing which identifies active infection and can be performed with massive throughput. The second is the logistics of gathering hundreds of thousands of samples to each testing laboratory each day.

Next Generation Solutions to COVID testing

Emerging technologies using targeted next-generation sequencing have been suggested as a potential solution to population-wide testing. The key features include 1) extraction free amplification 2) an easily collected specimen such as saliva, 3) nucleotide barcodes to enable sample pooling, and 4) a limited number of targets (to allow deeper sequencing, i.e. higher sensitivity). Illumina is selling a whole genome test for SARS-CoV-2, but this limits sequencing to 3,000 tests/ run. Another recent approval for a private testing lab uses only one target, and may allow it to increase to 100,000 tests/ day. And a recent protocol for LAMP-Seq in pre-print outlines how this could work in a scheme below. An attractive aspect of this approach is decentralized specimen processing.

Whereas Bill Gates has supported a portfolio approach to vaccines placing multiple bets on different processes in parallel, a similar approach should be applied to multiplexed sequencing methods. Two sequencing runs can be performed on a single instrument in a single day, which can process several thousand samples. However, sequencing is not the only step in sequencing; library preparation and specimen handling take significant amounts of time too.

Laboratory Logistics

This technology would represent an exponential expansion in analytic testing capacity, but clinical labs will require a similar escalation in logistic capacity. The largest clinical laboratories in the world process less than 100,000 samples per day. Clinical laboratories have a long history of automation with the first robotic specimen track systems developed in the 1980s. Engineering and clinical lab expertise should thus partner to innovate on methods to handle high volumes. This level of investment for an issue that is likely to fade in 2 years, is not attractive to most private health systems, so public investment from multiple states in regional reference labs is needed.

It is still hard to conceive the necessary scale up in sample processing can be achieve within the time frame needed, so I would also propose a de-centralized sample processing approach. This would include self-collection of saliva (a safe, effective sample type with similar sensitivity as nasopharyngeal swabs), drop-off sites, and processing at places like Pharmacies (>90% of Americans live within 5 miles of a pharmacy and they could be authorized to administer tests- just as they administer vaccines). This would introduce pre-analytic problems, but if the goal is frequent and high rates of testing, then we will have to accept certain losses in sensitivity (which currently is arguably better than it needs to be). Interestingly, pre-analytic concerns with saliva have not led to sample instability or degradation of RNA causing false negatives, as described in my last post. However, other factors could affect saliva quality: smoking, age, and genetic factors of water: protein ratio affecting viscosity.

Testing solutions should be considered in the context of the planned testing network. The specimen type should be easy for the patient to provide, processed with existing laboratory equipment and resulted electronically. For example, current COVID-19 testing is based on sample collections requiring a healthcare worker encased in personal protective equipment (PPE) utilizing a swab device. Testing needs to progress to a simpler solution such as saliva which can be collected by the patient in the absence of a swab or PPE. Preliminary studies have demonstrated that saliva is sample type comparable to nasopharyngeal swab. The ideal saliva sample would be collected into an existing collection tube type (e.g. red-top tubes) which are already compatible with existing laboratory automation. In aggregate, a person could spit into a tube at-home, have the tube sent to a laboratory, and in the laboratory the tube would be directly placed onto an automated robotic track system. 

Laboratory professionals need to provide a comprehensive plan for regional and national laboratory networks which can scale to provide overwhelming force to COVID-19 testing. No other profession or governmental organization understands testing as much as we do. Our understanding of managing samples from collection to result should be applied to the pandemic at hand. Until now most laboratorians in the US have focused on the immediate needs of providing testing for symptomatic patients and healthcare workers.

Vision for automated COVID-19 testing

One could envision an automated line of testing that moves samples through processing to allow multiplexing and combinations of samples to allow large numbers of patients to be tested at once (see below). This is feasible in some specialized centers, but would require investments in automation, bioinformatics, and interfaces for a seamless process (figure below). If testing mostly asymptomatic patients, it may also be possible to do this on pooled samples. The number of samples to pool would depend on the likelihood to having a positive result (this would require sequencing all individuals in a pool).

This represents a synthesis of ideas in decentralized specimen collection, laboratory automation and massive testing throughput with Next-Generation Sequencing, but unfortunately this is not yet a reality.

References

  1. Jonathan L. Schmid-Burgk et al. LAMP-Seq: Population-Sclae COVID-19 Diagnostics Using Combinatorial Barcoding. bioRxiv 2020.04.06.025635.
  2. The Rockefeller Foundation. National Covid-19 Testing Action Plan Pragmatic steps to reopen our workplaces and our communities. 2020.
  3. Cahill TJ, Cravatt B, Goldman LR, Iwasaki A, Kemp RS, Lin MZ et al. Scientists to Stop COVID-19.  OR Rob Copeland, Wall Street Journal (2020) The Secret Group of Scientists and Billionaires Pushing a Manhattan Project for Covid-19. April 27
  4. https://www.illumina.com/products/by-type/ivd-products/covidseq.html

-Jeff SoRelle, MD is a Chief Resident of Pathology at the University of Texas Southwestern Medical Center in Dallas, TX. His clinical research interests include understanding how the lab intersects with transgender healthcare and improving genetic variant interpretation.

Extraction-free and Saliva COVID-19 Testing

Much has changed quickly with SARS-CoV-2 virus (COVID-19) testing. Several commercial options are now available. Labs have less problems getting control material (positive samples are no longer in short supply). And labs that opted to bring on testing are now running multiple versions of COVID-19 molecular tests with a combination of high speed platforms or high throughput. Rapid cartridge tests are used for clearing people from the ED/ removing contact isolation on inpatients while the high throughput assays are used for routine screening.

However, several bottlenecks still exist. There are shortages of nucleic acid extraction kits, collection swabs and viral transport media. Fortunately, some recent studies have demonstrated preliminary evidence for using alternative sample types, collection methods, and storage conditions.

One of the first tenets of molecular diagnostics is isolation and purification of nucleic acid. Therefore, it was surprising to see a report on an extraction-free COVID-19 protocol from Vermont (Bruce EA et al.). This study initially analyzed two patient samples and showed drops in sensitivity of ~4Ct cycles. While this would not be suitable for low level detection, many viral samples have high levels of virus that still would permit detection. The team went on to test this method on 150 positive specimens from the University of Washington and found 92% sensitivity with 35% sensitivity at the low viral load range (Ct value> 30). This was improved with a brief heat inactivation step (Table 1). This was similarly seen in a study from Denmark, where brief heat inactivation of extraction-free methods (Direct) had 97% specificity in 87 specimens (Table 2).

Table 1. Vermont study comparing sensitivity of direct RT-PCR (no extraction step) with the validated results of 150 specimens coming from the University of Washington.
Table 2. Denmark study found extraction-free protocols (Direct) were comparable to extracted RNA (MagNA Pure extraction method) detection in 87 specimens.

Some similar studies out of Chile also showed extraction-free protocols on a larger number of specimens, and they reported a loss in sensitivity varying from 1-7 Ct cycles depending on the primers used.

Figure 1. P1 and P2 are patient 1 and 2. NSS indicates a nasal swab sample where RNA was extracted. RNA indicates a sample with no RNA extraction.

As this novel Coronavirus has an RNA-based genome, RNA is the target of molecular tests. As RNA is susceptible to degradation, there have been concerns over sample storage. Should it be refrigerated? Frozen? How do multiple freeze-thaw cycles impact specimen stability? Are there viable alternatives to viral transport media? One preliminary study explored these questions very nicely. They took X multiple sample types (NP, BAL, saline storage media) and stored them at 20C, 4C, -20, and -70 for multiple days up to 1 week and then analyzed the level of virus detected. In each case, the loss in sensitivity was minimal (<2 Ct cycles from day 0 to day 7) at room temperature with comparable results at lower temperatures (Table 3).

Table 3. Stability of SARS-CoV-2 RNA detected by the Quest EUA rRT-PCR. VCM- viral culture media; UTM-R Copan’s transport medium; M4-microtest media; BAL- bronchoalveolar lavage.

Lastly, alternative sample types such as saliva will help break the bottleneck in swabs and viral transport media. I was surprised to hear about this being a suitable alternative. Having worked with saliva for DNA analysis, I know it can be contaminated, of variable quantity, includes digestive enzymes and is viscous (slimy). These are not characteristics a lab would look for in a specimen type being used for high-throughput testing where several sample failures could occur. But these researchers from Yale showed measurable levels of SARS-CoV-2 that facilitated even higher sensitivity than nasopharyngeal swabs (Wylie AL et al).

Figure 2. SARS-CoV-2 titers are higher in the saliva than nasopharyngeal swabs from hospital inpatients. (a) All positive nasopharyngeal swabs (n = 46) and saliva samples (n = 39) were compared by a Mann-Whitney test (p < 0.05). Bars represent the median and 95% CI. Our assay detection limits for SARS-CoV-2 using the US CDC “N1” assay is at cycle threshold 38, which corresponds to 5,610 virus copies/mL of sample (shown as dotted line and grey area). (b) Patient matched samples (n = 38), represented by the connecting lines, were compared by a Wilcoxon test (p < 0.05). (c) Patient matched samples (n = 38) are also represented on a scatter plot.

With a much-needed increase in testing for this country, optimizations need to be implemented to improve efficiency. These steps alone will not be enough, but if we can have extraction-free testing of saliva collected at home, this would provide a substantial benefit to bringing easy testing to everyone.

UPDATE: Since this was written, the first FDA EUA was authorized for an at-home saliva collection kit for use at the Rutger’s clinical genomics lab (https://www.fda.gov/media/137773/download).

References

Please note: many of these references were on pre-print servers and have not been peer-reviewed.

  1. Bruce EA, Huang ML, Perchetti GA, et al. DIRECT RT-qPCR DETECTION OF SARS-CoV-2 RNA FROM PATIENT NASOPHARYNGEAL SWABS WITHOUT AN RNA EXTRACTION STEP. 2020. https://www.biorxiv.org/content/10.1101/2020.03.20.001008v2.full#T2
  2. Wyllie AL, Fournier J, Casanovas-Massana A, Campbell M et al. Saliva is more sensitive for SARS-CoV-2 detection in COVID-19 patients than nasopharyngeal swabs. medRxiv 2020. https://www.medrxiv.org/content/10.1101/2020.04.16.20067835v1#disqus_thread
  3. Fomsgaard AS, Rosentierne MW. An alternative workflow for molecular detection of SARS-CoV-2 – escape from the NA extraction kit-shortage, Copenhagen, Denmark, March 2020. https://www.medrxiv.org/content/10.1101/2020.03.27.20044495v1.full.pdf
  4. Rogers AA, Baumann RE, Borillo GA, et al. Evaluation of Transport Media and Specimen Transport Conditions for the Detection of SARS-CoV-2 2 Using Real Time Reverse Transcription PCR. JCM 2020.
  5. Beltran-Pavez C, Marquez CL, Munoz G et al. SARS-CoV-2 detection from nasopharyngeal swab samples without RNA extraction. bioRxiv 2020. https://www.biorxiv.org/content/10.1101/2020.03.28.013508v1.full.pdf

-Jeff SoRelle, MD is a Chief Resident of Pathology at the University of Texas Southwestern Medical Center in Dallas, TX. His clinical research interests include understanding how the lab intersects with transgender healthcare and improving genetic variant interpretation.

Introduction to Short Tandem Repeat

Hello again!

I hope everyone is staying safe and healthy during these unfortunate times. My last post was in relation to being a new MLS grad and beginning my career as a molecular technologist at Northwestern University’s Transplant Lab. Time definitely flies by!

Today I’m going to provide a basic introduction on an assay I’ve recently been trained on called Short Tandem Repeat (STR). If you were to take a glance at your genome, it would be littered with many repeating sequences. While there are many different classifications of repeating sequences, STRs are a type of tandem repeating sequence where each repeat is approximately 2 to 7 nucleotides in length.1,2,3 STR is well-known in forensic science to help identify a suspect at a crime scene when different sources of DNA are present. Yet, its applications are many – from cell line confirmation, paternal testing, and all the way to chimerism analysis!4

Image 1. Electropherogram depicting two different alleles (11 and 17) within 1 locus (D6S1043). Allele 11 has 11 repeats and allele 17 has 17 repeats.

STRs are polymorphic, one useful characteristic among many, which make its utilization in identifying the source of DNA particularly advantageous. An STR allele is defined by the number of times the repeating sequence, defined above, repeats. (Image 1).1 Individuals are either heterozygous or homozygous at each locus. As the number of STR loci being evaluated increases, the statistical power of discrimination increases and the likelihood of another individual having the same profile becomes increasingly unlikely and detecting small differences increases.3,4 In our lab, we evaluate a total of 21 different loci!

Additionally, in our HLA lab we utilize STR to monitor chimerism status in patients who have undergone an allogeneic stem cell transplant. Before their transplant, patients are matched to a donor through their HLA system (different from STR). Once an HLA match is confirmed, we utilize the patient’s pre-transplant and the donor’s sample to generate STR informative alleles. Informative alleles are alleles that are present only in the recipient and not the donor. These alleles are important because stem cell transplants replace the recipient’s marrow and the detection of recipient DNA in post-transplant samples is crucial to identifying rejection or relapse of their disease. Additionally, loci that contain informative alleles are defined as informative loci, these are the loci then used to identify the percentage chimerism (Image 2).

Image 2. Donor and recipient (pre-transplant) are represented in the first two electropherograms. The green “D1R” tags represent shared alleles, the blue “D1” tags represent donor specific alleles, and the brown “R” tags represent recipient specific alleles. In the first locus, AMEL, there are no informative alleles and therefore it is not an informative locus. In the next locus, D3S1358, there is one shared allele, 15, one donor allele, 17, and one recipient informative allele, 18. Informative loci have recipient informative alleles and can detect the presence of recipient DNA in a sample – in this case all of the following loci after AMEL are informative loci. CD3 (post-transplant) is represented on the third electropherogram. In this example, it is clear that the patient is having some sort of graft failure or reoccurrence of their disease because their own cells, instead of just the donor, are present.

When recipient cells begin to re-emerge, we can detect the relative allele peaks and assign them to the recipient or donor by referring to the informative alleles. Allele peaks are then utilized through equations in our software that measure the area under these defined peaks and then compute a donor percentage chimerism. Once that informative report is created, we can compare any proceeding post-transplant sample to determine the patient’s chimerism status (Image 2).

Interesting enough, we don’t simply isolate the DNA from the post-sample buffy like we would with other samples. Rather, we separate each post sample into a total of three sub-samples. The first is simply the patient’s peripheral blood – nothing fancy. The other two are isolated from the rest of the peripheral blood that was not used into two separate cell lineages – lymphocytes (CD3+) and myelocytes (CD33+). This process is extremely labor-intensive, being able to process a set of up to 8-12 patients at a time and each set taking up to 4-5 hours.

The process begins by aliquoting peripheral blood for DNA isolation (sample 1) and taking the remainder and layering it over a lymphocyte separation medium (LSM). Then harvesting the lymphocyte/white cell layer from the spun down LSM. We then go on to add CD3 and CD33 antibody selection cocktails and magnetic beads. Then, we do a series of washes with magnets and eventually end up with our purified CD3 and CD33 cell populations. Their purity is determined through flow cytometry, an important component to confirm that our leukocyte subsets aren’t contaminated with other leukocyte populations – as contamination would defeat the purpose of analyzing different lineages.

Finally, we take the isolated DNA from the three sub-samples and amplify it with specific primers and fluorescent tags through PCR. Then the samples are loaded onto a capillary electrophoresis instrument. This instrument will detect each fragment length, defined by the primers and the repeats within, and be able to identify these fragments through size, fluorescent tags, lasers, and detectors. The instrument will then generate data that we can take to our analyzing platform, which is ChimerMarker. Through this we can analyze the data and generate our clinical reports.

Though extremely time intensive, lineage-specific chimerism is critical in stem cell transplant because it is more informative and sensitive than total leukocyte analysis – being several magnitudes more sensitive than analyzing just peripheral blood alone. It permits early detection of small chimeric cell populations that otherwise may go undetected, as one subset in the peripheral blood may “mask” another subset that has increasing percent recipient cells. Diagnosing these small cell chimeric cell populations as early as possible is critical for therapeutic interventions and reductions in graft rejections.2,5,6

Furthermore, not only is their detection important, but through our analysis we can calculate the percentage of donor cells and recipient cells. We oftentimes report out the donor percentage (%) chimerism. For example, a patient at 322 days post-transplant could have a donor chimerism of 96% in their peripheral blood, 100% in their CD33 lineage, and 73% in their CD3 lineage. Then, at day 364 post-transplant they may then be at 100% in their peripheral blood, 100% in their CD33 lineage, and 92 percent in their CD3 lineage. Two things to notice in this example is that the percentages are changing (increasing in donor chimerism in this case) and that the peripheral blood expressed 100% chimerism in the second sample at 364 days, but when we look specifically at the CD3 sub-population at 364 days there was still 8% of recipient cells present (Image 3 & 4).

Image 3. Samples at 322 days post-transplant. Peripheral blood reports 96% donor chimerism. CD3 and CD33, purified from peripheral blood, reports 73% and 100% donor chimerism, respectively.
Image 4. Samples at 364 days post-transplant, same patient as in Image 3 above. Peripheral blood reports 100% donor chimerism. CD3 and CD33, purified from peripheral blood, reports 92% and 100% donor chimerism, respectively.

Some studies have focused not only on the trends in percentages changing, but also in their relative percentage constellation. For example, one study found that increased recipient CD3 cells had an increased predictive factor of graft rejection. It was also found that further sub-leukocyte populations increased this predictive power.5 Even more, there have been some studies that have looked at chimerism and its usefulness in predicting graft versus host disease (GvHD). This disease is defined by donor leukocytes attacking the leukocytes and tissues of the recipient. Through these and other findings, the potential and applicability of chimerism monitoring is extremely crucial to patient care during their transplant progression.2,5,6,7

While engraftment is a very dynamic process, varying from individuals and disease-types, engraftment monitoring is one way to monitor and ultimately influence therapeutic approaches.2,5,6 I am proud to be able to contribute to the wonderful team here at Northwestern University and I strive to learn more about the process – both clinical and in the lab. In future articles, I hope to go into more detail about the process and other assays that we perform.

Thanks for reading! Until next time! Stay well and safe during these uncertain times!

References

  1. Life Technologies. 2014. DNA Fragment Analysis by Capillary Electrophoresis. Thermo Fisher Scientific. http://www.thermofisher.com/content/dam/LifeTech/global/Forms/PDF/fragment-analysis-chemistry-guide.pdf.
  2. Kristt, D., Stein, J., Yaniv, I., & Klein, T. (2007). Assessing quantitative chimerism longitudinally: technical considerations, clinical applications and routine feasibility. Bone Marrow Transplantation, 39(5), 255–268. doi: 10.1038/sj.bmt.1705576
  3. Clark, J.R., Scott, S.D., Jack, A.L., Lee, H., Mason, J., Carter, G.I., Pearce, L., Jackson, T., Clouston, H., Sproul, A., Keen, L., Molloy, K., Folarin, N., Whitby, L., Snowden, J.A., Reilly, J.T. and Barnett, D. (2015), Monitoring of chimerism following allogeneic haematopoietic stem cell transplantation (HSCT): Technical recommendations for the use of Short Tandem Repeat (STR) based techniques, on behalf of the United Kingdom National External Quality Assessment Service for Leucocyte Immunophenotyping Chimerism Working Group. Br J Haematol, 168: 26-37. doi:10.1111/bjh.13073
  4. Short Tandem Repeat Analysis in the Research Laboratory. (2012). Retrieved April 10, 2020, from https://www.promega.com/resources/pubhub/short-tandem-repeat-analysis-in-the-research-laboratory/
  5. Breuer, S., Preuner, S., Fritsch, G., Daxberger, H., Koenig, M., Poetschger, U., … Matthes-Martin, S. (2011). Early recipient chimerism testing in the T- and NK-cell lineages for risk assessment of graft rejection in pediatric patients undergoing allogeneic stem cell transplantation. Leukemia26(3), 509–519. doi: 10.1038/leu.2011.244
  6. Buckingham, L. (2012). Molecular diagnostics: fundamentals, methods, and clinical applications. Philadelphia: F.A. Davis Company.
  7. Rupa-Matysek, J., Lewandowski, K., Nowak, W., Sawiński, K., Gil, L., & Komarnicki, M. (2011). Correlation Between the Kinetics of CD3 Chimerism and the Incidence of Graft-Versus-Host Disease in Patients Undergoing Allogeneic Hematopoietic Stem Cell Transplantation. Transplantation Proceedings43(5), 1915–1923. doi: 10.1016/j.transproceed.2011.02.011

-Ben Dahlstrom is a recent graduate of the NorthShore University HealthSystem MLS program. He currently works as a molecular technologist for Northwestern University in their transplant lab, performing HLA typing on bone marrow and solid organ transplants. His interests include microbiology, molecular, immunology, and blood bank.

Tips for COVID-19 Testing

Since I last wrote about some testing options available for COVID-19 testing just 1 month ago, many things have changed in the regulatory requirements, and the companies offering testing options. With that in mind along with the fact that things will likely continue to changes, I’ll write to address current and future challenges facing COVID-19 laboratory testing.

  1. What control material can be used?
  2. How can I make specimens safe?
  3. Supply chain issues and solutions.
  4. False Negative results of COVID-19 tests: what to tell clinicians.
  5. Serology Tests: Future Testing and Challenges

Control Material

As the FDA said contrived specimens could be used, that means that RNA can be spiked into a clinical matrix for extraction. While this began with a requirement for genomic RNA, it has been loosened to include plasmid DNA. However, I would caution against using plasmid DNA, because when it is amplified, it can easily cause contamination and unlike RNA, DNA can persist in the environment for a long time. I once hear a story about a lab director who thought they were very careful, but in pipetting, they contaminated the lab in 3 days and it had to be cleaned up for 4 weeks.

We had some issues using in vitro transcribed RNA (of just the N-gene) and genomic RNA, because the recovery was very low. We found out that intact viral particles were better in optimization experiments using control endemic SARS strains (Zeptometrix controls, Table 1). The free RNA Ct values fell sharply (over 1000-fold) when added to Nasopharyngeal (NP) matrix or Viral Transport Media (VTM). However, much lower levels of the encapsulated viral control had consistent levels of amplification.




Table 1. Amplification of free viral RNA vs. viral particles when added to matrix

Therefore, we used a synthetically encapsulated SARS-CoV-2 RNA sample called Accuplex (SeraCare, Figure 1), which gave good recovery and a limit of detection down to 260 copies/ mL (5 copies/ reaction). Alternative similar material that we have not evaluated include: COVID-19 RNA synthesized inside inactivated E coli (Zeptometrix) and Armored RNA (Asuragen).

Figure 1. Schematic of how a synthetically created viral particle occurs

Lab Safety of Specimens

A safety recommendation of the FDA was to perform extraction of samples in a Biosafety level 2 hood. However, high-throughput extraction can’t be easily done this way. For us, we had to prepare samples in the hood then take them to the stand-alone closed system extractor. Our Micro fellow had the creative idea to do “Off-Board” lysis, which would inactivate the virus in the hood before walking it over. We later found that combining lysis with NP matrix before spiking RNA stabilized the RNA for accurate measurement. We were able to find an LOD of 14 copies/ reaction this way.

Some labs have proposed using heat inactivation (~30 minutes at 50-60C) of virus as a safety measure, but the published literature available on how that affects sensitivity is lacking currently.

Supply Chain issues

You have surely heard about all of the new companies that have come out with new testing platforms and assays for COVID-19 testing by now. However, the downside is that unless you already have their instrument, you likely won’t be able to get reagents in time to perform the assay. Even if you do have an instrument, limited resources are necessitating allocation based on high risk areas, so you are likely to receive fewer kits than you would like. Also, the reference labs are still ramping up capacity and are returning results back with long turnaround times currently (~ 1 week). This supports the strategy to bring the testing in-house, so that you can get results back quickly and have control over at least your labs reagent supply. If you have the instrumentation of another FDA approved EUA, you can start performing testing if you follow that protocol exactly- the CDC is the most widely used.

False Negative Tests of COVID-19

This is hard to assess when only one lab testing modality (PCR) is available, but clinicians report negative results in a patient with classic symptoms and a contact history with a COVID-19+ person. Given the impressive analytic sensitivity of the test (generally 1 copy of RNA in 1mL of sample), the likely explanation is that there is a specimen issue. Proper NP sampling requires sticking the swab to the very back of the nasal cavity. Furthermore, this virus may reside more in the lower respiratory track (lungs) and simply not be present in the area sampled. This is why repeat sampling could be helpful. However, the outcome should be the same whether or not you have a negative test: if you have symptoms you should self-isolate unless you require emergent care due to shortness of breath or other symptoms that can’t be managed at home. The lab is familiar with these pre-analytic limitations that can arise, but it is helpful to explain this to clinicians.

Serology Tests: Future Testing and Challenges

Serology can be very helpful as a separate method from qPCR to determine if someone has been infected with SARS-CoV-2. Notice, that is in the past tense. A small (n=9) pre-print study from Nature indicates serologic conversion starts around day 8 or 10 after symptom onset, which often is not in a clinically helpful timeframe. However, these tests are cheaper and easier to perform, so could be useful for epidemiological purposes to determine who has been infected with COVID-19. Early genetic data indicates that the mutation rate is slow (4x slower mutation rate compared to seasonal flu) as one would suspect for RNA-based viruses, so the virus shouldn’t change enough to cause re-infection in someone with sufficient antibody levels.

Figure 2. Scheme of the first COVID-19 antibody test to receive FDA Emergency Use Authorization.

However, several challenges in interpreting these antibody tests include:

  1. Some conflicting data as to how quickly IgM develops relative to the onset of symptoms
  2. What is the time-line for IgG production?
  3. Ruling out cross reactivity with other strains of Coronavirus that cause upper respiratory infections.

References

  1. Wolfel R, Corman VM, Guggemos W et al. Virological assessment of hospitalized patients with COVID-2019. Nature epub ahead of print. https://www.nature.com/articles/s41586-020-2196-x_reference.pdf
  2. Mitchell S, George K et al. Verification procedure for commercial tests with Emergency Use Authorization for the detection of SARS-CoV-2 RNA. American Society of Microbiology
  3. https://www.livescience.com/coronavirus-mutation-rate.html

-Jeff SoRelle, MD is a Chief Resident of Pathology at the University of Texas Southwestern Medical Center in Dallas, TX. His clinical research interests include understanding how the lab intersects with transgender healthcare and improving genetic variant interpretation.

How to Validate a COVID-19 Assay

The FDA is now democratizing the testing of the novel coronavirus: SARS-CoV-2 (the virus which causes the COVID-19 disease syndrome—I will call it COVID-19 from here on as that is the colloquial name most people know) by allowing high complexity testing labs across the United States. This move will permit more labs to test for COVID-19. A previous post by contributor Constantine Kanakis describes the biology of the virus, so I will not repeat that material. Instead, I will focus on some considerations in validating a Lab Developed Test (LDT) COVID-19 molecular assay.

The president of AACC, Carmen Wiley, said there are 11,000 high complexity testing labs in the US, which could qualify for performing this testing. However, not all of these labs have molecular and virology expertise, so others have placed the number of labs with qualified staff and instrumentation at 400.

Published Assays and Targets: As an overview, the figure below (Figure 1) summarizes some published COVID-19 assays. As you can see, the major strategy involves using the TaqMan probe strategy where a short probe is degraded by Taq polymerase releasing a fluorescent molecule (green ball) from a quencher molecule (blue ball). The TaqMan approach allows for quick performance of the assay and easy interpretation. One lab from Japan is using nested PCR amplification and sequencing of the Orf1a and S genes as well.

Figure 1. The COVID-19 genetic structure is abbreviated above with the different genes targeted displayed. The names of institutions that have published their assay procedure along with the TaqMan reagents that were reportedly used with each assay are shown above. Primers are represented by small arrows with a TaqMan probe in the middle represented by a black line with green and blue circles indicative of the fluorescent molecule and its quencher. The double set of arrows for the Japanese assay represents a nested PCR strategy.

In silico Cross-reactivity:

The FDA guidance allows cross-reactivity to be minimally assessed in silico by demonstrating “greater than 80% homology between primer/probes and any sequence present in the targeted microorganism.” The primer locations can be found in the publication of each protocol (except Thermo) and can be confirmed by checking the NCBI Blast site and they actually have a selection for beta-cornavirus (Figure 2) now that allows you to search for your primer’s reactivity across other related viruses- Very helpful!

Figure 2. Select Betacornavirus before entering your primer/probe sequence to confirm cross-reactivity.

Primer/Probe Design:

The N region is the most popular site to probe and is included in most kits once and the CDC kit three times. It was the reagent set for N3 in the CDC kit that was having difficulties, so you may decide to not include that component in your LDT. If you want to see how the different available primer sets align on the N gene sequence you can see below for the primers labeled based on their source. Many are overlapping, perhaps because many people thought the same site was a good target (Figure 3).

Figure 3. N-gene of COVID-19 along with labeled primers from some published assays. The information on the source of the sequence is shown on the bottom right with the link.

Commercially Available Assays:

An important part of validating your COVID-19 assay is to do so quickly. Thus commercially available kits would be helpful, however there are only two commercially available sources at this time: IDT and Thermo. IDT is producing a kit with the CDC design. Thermo produced their kit over the last few months and does not have any published validation information that I could find. Also Thermo when I checked just now for the catalog number, it says this product is unavailable… not sure what that means, but maybe you can try contacting them. Both IDT and Thermo list control plasmid reagents for their assays.

Controls for the Assay:

The wording of the FDA announcement was interesting in that it 1) did not require clinical samples, but allows “contrived clinical specimens.” “Contrived reactive specimens can be created by spiking RNA or inactivated virus into leftover clinical specimens.” A major difficulty is the access to actual COVID-19 RNA or inactivated virus. I noticed that the guidance didn’t say that the assay MUST use RNA. Thus most labs would have access to plasmid DNA, which could potentially be used.

Given the limited availability of RNA for validation use, a lab may consider performing much of the assay optimization with COVID-19 Plasmid DNA while waiting for access to RNA. I would like to be sure my assay could extract, amplify and detect RNA as part of the clinical validation.

Asuragen can produce Armored RNA, with synthetic RNA packaged inside of a viral capsid, which would be a useful control for extraction, amplification and detection. However, we heard this will not be available for another month.

Tom Stenzel (director of the Office of In Vitro Diagnostics and Radiological Health at the FDA’s Center for Devices and Radiological Health (CDRH)) said FDA, BARDA, and the CDC will prioritize and coordinate shipments of viral materials to labs when they are ready to validate tests according to a webinar with labs on Monday. Currently, the FDA is directing inquiries to BEI, which is reportedly prioritizing requests to send out samples in 12-72 hours.

Lastly, one could try to use in vitro synthesized RNA sequences surrounding your primer targets as a control for now and may have better luck in getting the product soon. This is the control that is being shipped with the CDC kits to public labs.

Limit of Detection is an unknown for what is likely to be clinically relevant as we don’t know what the levels look like in people with early vs. late vs. severe vs. mild disease. The FDA just says you should be able to detect 95% of samples (19 of 20) that are x1-x2 the limit of detection.

FDA Notification:

This is the final and important step. Once you go live, you must notify the FDA with an Emergency Use Assay (EUA) form within 15 days. Reviewing the form, there doesn’t appear to have complex explanations or overdue requirements for reporting, which wouldn’t be found in a standard lab validation document.

Final Thoughts/Future commercial solutions:

This information is the best of what I know right now based on current information- this is not a complete guide and the FDA guidance should be read closely for all compliance details. Information is changing quickly and is likely to change more if the number of COVID-19 cases in the United States increases. Cepheid, Luminex, and BioFire are reportedly working on assays that will be out in several months and would be easy to use for many labs that already have one or both of these systems-however it may require a full validation for an LDT, but I’m not sure as it is an EUA-further clarification on this point is needed. Although there are several commercial solutions available, we don’t know how demand could impact supply from each company. Fortunately, some large reference labs like LabCorp and Quest are looking to develop a COVID19 test. Good luck, stay safe, and feel free to contact me with any questions in the comments below so that everyone can benefit from the discussion!

References

In lieu of a list of references, I’ve included web links for the most current and direct sources of information.

-Jeff SoRelle, MD is a Chief Resident of Pathology at the University of Texas Southwestern Medical Center in Dallas, TX. His clinical research interests include understanding how the lab intersects with transgender healthcare and improving genetic variant interpretation.

Biomarker Testing for Cancer Patients: Barriers and Solutions Part 3

This month we will continue discussing the common barriers to biomarker testing for cancer patients in the community.

As you may recall, these are the top 10 barriers that I’ve seen to biomarker testing in the community:

  1. High cost of testing.
  2. Long turnaround time for results.
  3. Limited tissue quantity.
  4. Preanalytical issues with tissue.
  5. Low biomarker testing rates.
  6. Lack of standardization in biomarker testing.
  7. Siloed disciplines.
  8. Low reimbursement.
  9. Lengthy complex reports.
  10. Lack of education on guidelines.

As I mentioned last month sample quantity and quality are both important when considering biomarker testing. We covered tissue quantity issue last month; let’s move on to tissue quality issues. I will focus on what happens to the tissue prior to testing being performed, called the preanalytical phase of testing. We now know that preanalytical variables can alter protein structure, DNA, and RNA (1). This can alter the results that are used to diagnose and treat patients. Despite the impact to downstream assays, this area is typically poorly controlled. Some of the sources of variance due to preanalytical processes include procurement, fixation, processing, and specimen storage (1).

Procurement:

ROSE: I covered rapid onsite evaluation (ROSE) during procurement last month with regards to tissue quantity. Having a pathologist evaluate both tissue quality and sufficiency during the biopsy is invaluable. For molecular analysis, areas of necrosis should be avoided.

Fixation:

Time to get specimen into fixation (cold ischemic time): Tissue begins to degrade as soon as it is removed from the body. The amount of time between removing tissue from the body and fixing it is referred to as the cold ischemic time. This time should be as short as possible. Less than 1 hour is recommended if molecular studies are going to be performed on the specimen (1). Tissue begins degrading immediately and this degradation can affect the results of biomarker test such as IHC & FISH (1). I’ve seen cases where the biopsy was collected, but due to a busy day in the OR, it was not sent to pathology immediately. This can cause the tissue to be so degraded that testing cannot be performed. Unfortunately, sometimes we don’t know there was a fixation issue until the molecular assay fails repeatedly. This is an expensive way to determine something went wrong in the preanalytical phase.

For small biopsies such as core needle biopsies or even fine needle aspirates, one way to decrease time to get the specimen into fixative is by having the fixative in the suite where the biopsy is collected so that it is put into fixative immediately. This won’t work for large pieces of tissue that may need to be dissected for optimal fixation penetration. For these biopsies, diligence needs to be taken to get the biopsy to the laboratory as soon as possible. Multidisciplinary communication will help ensure the hand-off occurs in a timely manner. Specimens may need to be dissected for optimal fixation penetration.  Other specimens may need to be decalcified prior to fixation.  

Decalcification: Most decalcification processes with formic acid have negative downstream effects on molecular testing. We have about a 50% success rate of PCR actually being able to amplify DNA after standard decal due to degradation. The solution to this is to use EDTA-based decalcification; however this could lengthen the fixation time drastically. Some new gentle decals are on the market that could be used without increasing the turnaround time.

Proper Fixative: We also need to ensure specimens are fixed in the appropriate fixative. The most common and widely accepted fixative is 10% neutral buffered formalin (NBF).  DNA yield and some downstream biomarker tests are negatively impacted if unbuffered formalin is used (1). Tissue fixation in alcohol such as 70% ethanol may be even better than NBF if the downstream assay involves DNA extraction; however ethanol fixation may negatively impact IHC or FISH assays (2).

Time in Fixative: Studies show that the appropriate amount of time a biopsy needs to be in fixative is about 6-72 hours (1). The wide range of times is due to the range of specimen sizes, it is generally accepted that formalin penetrates tissue at the rate of 1 mm/hour (3). Tissue may need to be dissected to ensure complete fixation within a reasonable time. If the tissue is not fixed appropriately, the tissue will degrade. However, too much time in fixative can lead to degraded DNA.

Downstream biomarker assays such as FISH, PCR, and ISH can be affected if the fixative time is greater than 72 hours (1). Small community sites that do not have someone processing specimens over the weekend may need to adjust their biopsy schedules on Fridays to ensure specimens do not sit in fixative for more than 72 hours. Unfortunately, unless the specimen is a breast biopsy, in which CAP requires fixation times to be documented and controlled, fixation times are rarely documented and controlled. This is an area we could all improve on. It would be nice to know how long a specimen was stored when we are troubleshooting a downstream assay.

Processing:

The impact of processing variables on biomarker testing has not been well published. One variable that has been called out as having a negative effect on PCR is mixing beeswax with paraffin wax. Only pure paraffin wax should be used. Other changes to the processing schedules should be performed with coordination between departments. If the anatomic pathology laboratory makes changes to their process, a verification study on the impact to the downstream assays should be performed. How extensive that study is should be determined by the medical director.

Specimen Storage:

As long as the specimen was properly fixed, FFPE block storage is normally fairly hearty. The literature recommends blocks that are used for molecular analyses be less than 10 years old (1). Although I wouldn’t recommend using blocks older than 10 years, cases positive for some biomarkers are rare, so during our validations some blocks used were over 10 years old, and the downstream PCR-based assays still worked. However, I have no way to know if the DNA yield was compromised.

Unlike FFPE blocks, long-term storage of FFPE slides does affect downstream testing (4). Room-temperature storage seems to be worse than refrigerated storage of slides. Slides should be used for IHC and biomarker testing relatively quickly (< 30 days).

Unfortunately I cannot cover all sources of preanalytical error thoroughly in a 1,000 word blog post, but hopefully this sparks your interest enough to check out the references where the authors give a more detailed explanation of preanalytical issues.

References

  1. Bass BP, Engel KB, Greytak SR, Moore HM. A review of preanalytical factors affecting molecular, protein, and morphological analysis of formalin-fixed, paraffin-embedded (FFPE) tissue: how well do you know your FFPE specimen? Arch Pathol Lab Med. 2014;138:1520-30.
  2. Lindeman NI, Cagle PT, Aisner DL, Arcila ME, Beasley MB, Bernicker EH, et al. Updated Molecular Testing Guideline for the Selection of Lung Cancer Patients for Treatment With Targeted Tyrosine Kinase Inhibitors: Guideline From the College of American Pathologists, the International Association for the Study of Lung Cancer, and the Association for Molecular Pathology. Arch Pathol Lab Med. 2018;142:321-46.
  3. Howat WJ, Wilson BA. Tissue fixation and the effect of molecular fixatives on downstream staining procedures. Methods. 2014;70:12-9.
  4. Economou M, Schoni L, Hammer C, Galvan JA, Mueller DE, Zlobec I. Proper paraffin slide storage is crucial for translational research projects involving immunohistochemistry stains. Clin Transl Med. 2014;3:4.   

-Tabetha Sundin, PhD, HCLD (ABB), MB (ASCP)CM,  has over 10 years of laboratory experience in clinical molecular diagnostics including oncology, genetics, and infectious diseases. She is the Scientific Director of Molecular Diagnostics and Serology at Sentara Healthcare. Dr. Sundin holds appointments as Adjunct Associate Professor at Old Dominion University and Assistant Professor at Eastern Virginia Medical School and is involved with numerous efforts to support the molecular diagnostics field. 

Biomarker Testing for Cancer Patients: Barriers and Solutions, Part 2

As you may recall last month I shared common barriers to biomarker testing for cancer patients in the community. I also began to dive-in to a few solutions that I have seen implemented to overcome the barriers. Last month I shared solutions that may help with high cost and long turnaround times for biomarker testing. This month I would like to discuss issues with tissue including quantity.

Here are the top 10 barriers that I’ve seen to biomarker testing in the community:

  1. High cost of testing.
  2. Long turnaround time for results.
  3. Limited tissue quantity.
  4. Preanalytical issues with tissue.
  5. Low biomarker testing rates.
  6. Lack of standardization in biomarker testing.
  7. Siloed disciplines.
  8. Low reimbursement.
  9. Lengthy complex reports.
  10. Lack of education on guidelines.

Sample quantity and quality are both important when considering biomarker testing. If we don’t have enough material we cannot perform the test (quantity not sufficient or QNS). If we have poor quality we cannot trust the results. The old adage of garbage in garbage out holds true for biomarker testing just as it does for all other lab tests.  

I’ll start with sample quantity this month and cover quality issues next month. The issue here is that a variety of biopsy types are performed on patients depending on the location and size of a suspicious mass. Historically we only needed enough material for the pathologist to make a diagnosis. Now we often need enough material for diagnosis and biomarker testing. Some tumor types such as breast and ovarian cancers produce enough material in locations that are easily accessible that tissue quantity is rarely an issue, however other tumor types such as lung and pancreatic cancers there is often an issue with tissue quantity. These tumor types must be handled with care to ensure no tissue recovered is lost.

The first step in addressing tissue insufficiency is knowing where you are starting. Do you have an issue with quantity not sufficient (QNS) rate? If you don’t know how many of your cases are insufficient for biomarker testing, then you can’t determine if you have an issue. If your testing is performed at a reference laboratory, you can request your QNS rate from the lab. They may also be able to provide you with the national QNS rate and then you could benchmark yourself against your peers. It is important to have an accurate QNS rate, so if there are blocks that are not sent to the reference lab because the pathologist has determined the block to be exhausted (no tissue is left) then the QNS rate provided by the reference lab may be artificially low.

It is important to agree upon what is QNS. We consider a specimen to be QNS if we cannot perform biomarker testing on the block. Others may consider the block QNS only if there wasn’t sufficient material for diagnosis. We have to ensure there is enough tumor content in the tissue to proceed with biomarker testing, in our case 10% of the nucleated cells (not volume) must be tumor (determined by pathology review of an H&E slide). If we have enough tumor, we can still end up with a QNS block due to low DNA and RNA yield. So we need sufficient tumor and sufficient tissue. 

Here is a brief overview of solutions I have seen work to address limited tissue that can lead to high QNS rates:

  • Education. The person collecting the biopsy needs to understand how much material is needed. Remember we have moved the goal post. Sufficient material for diagnosis was enough in the past, now we need more material to perform biomarker testing. Educating the team on why we need more material is valuable in ensuring sufficient material is collected.
  • ROSE. Rapid onsite evaluation (ROSE) by a pathologist in the procedure room to determine sufficiency has been shown to decrease the repeat biopsy rate [1]. The pathologist can ensure the biopsy is being collected in a tumor rich region and help ensure areas of necrosis are avoided.  
  • Embedding cores separately. We often get core needle biopsies on lung cancer specimens. We prefer 3-5 cores. It is best practice to independently embed the cores in separate blocks. I have also seen labs that embed no more than 2 cores in one block. This would allow one block to be conserved for diagnosis and the other to be used for biomarker testing.
  • Visual cue for limited tissue. Someone far more creative than me developed a process in histology where in cases of limited tissue the tissue was embedded in a red cassette. This cassette color was a visual cue for everyone handling the block that the tissue was limited and care should be taken when facing into the block. This has evolved over time to a red bead being embedded beside the tissue. Any visual cue and an associated procedure to ensure tissue conservation can help ensure we are conserving tissue in cases where it matters.
  • Limited IHC Stains. The primary reason a biopsy is performed is for diagnosis. It is recommended that as few IHC stains as possible be used to make the diagnosis. This will conserve tissue for biomarker testing.
  • Unstained Slides. Cutting 15-20 unstained slides is considered best practices in tumor types such as lung where biomarker testing will be performed within 30 days. Long term storage of unstained slides is not recommended.
  • Reduce the number of times the block goes on the microtome, because every time the block is put back on the microtome it must be refaced. This results in wasted tissue. This can be prevented by thinking ahead and cutting everything you know will be needed while the block is on the microtome.

References

  1. Collins BT, Murad FM, Wang JF, Bernadt CT. Rapid on-site evaluation for endoscopic ultrasound-guided fine-needle biopsy of the pancreas decreases the incidence of repeat biopsy procedures. Cancer Cytopathol. 2013;121:518-24.

-Tabetha Sundin, PhD, HCLD (ABB), MB (ASCP)CM,  has over 10 years of laboratory experience in clinical molecular diagnostics including oncology, genetics, and infectious diseases. She is the Scientific Director of Molecular Diagnostics and Serology at Sentara Healthcare. Dr. Sundin holds appointments as Adjunct Associate Professor at Old Dominion University and Assistant Professor at Eastern Virginia Medical School and is involved with numerous efforts to support the molecular diagnostics field. 

Biomarker Testing for Cancer Patients: Barriers and Solutions, Part One

We are seeing an unprecedented amount of new targeted therapies for cancer treatment that are tied to diagnostic tests. Drug companies are heavily invested in ensuring the right patients get the right therapy. This is because it actually benefits pharma companies and patients. Patients get a very specific therapy that will likely improve their survival rate and improve their quality of life. By being selective and targeting only patient populations that are likely to respond based on the biology of their tumor, pharma companies show improvements over existing therapies which supports their request for FDA-approval.

With every pharma company tying their drug to specific rare biomarkers, broad molecular profiling such as NGS becomes more important than ever. We will never find the needle in the haystack if we don’t examine the entire stack. However, most cancer patient care occurs in the community where NGS testing is not usually offered locally. There are specific barriers to biomarker identification in the community setting. I will take the next few months to discuss specific barriers and how a lab might overcome these obstacles in order to increase patient access to precision medicine. Just as no barrier is identical between institutions, no solution will be one-size fits all. Feel free to cherry pick and modify solutions that you feel would address your local issues. Remember don’t let perfect be the enemy of the good. Small incremental improvements are impactful and generally require fewer resources than trying to revamp your entire process.

Here are the top 10 barriers that I’ve seen to biomarker testing in the community:

  1. High cost of testing.
  2. Long turnaround time for results.
  3. Limited tissue quantity.
  4. Preanalytical issues with tissue.
  5. Low biomarker testing rates.
  6. Lack of standardization in biomarker testing.
  7. Siloed disciplines.
  8. Low reimbursement.
  9. Lengthy complex reports.
  10. Lack of education on guidelines.

This month I will address the first two barriers that I commonly see with respect to biomarker testing. Molecular testing is expensive and turnaround time is often long. This was especially true for technology such as NGS. There are a few solutions to the high cost and long turnaround time for molecular testing that I’ve seen work well.

Solutions to costly molecular testing such as NGS:

  1. Insource NGS testing.
  2. Continue to send-out but renegotiate your contracts with reference laboratories to ensure pricing is as low as possible.

Let’s dig into the decision to insource NGS versus continuing to outsource testing. It’s easy for me to say insource the test and describe the benefits of doing so, but if your volume is low and you don’t have the facility or expertise, this solution is not likely to work for you. There is a new platform coming to market that claims to make it easier to insource NGS without extensive molecular expertise, however the company will need to provide data to support that claim. If they do show they can provide NGS testing with less expertise, then this could be a game changer for community labs looking to insource NGS testing.  

The benefits of insourcing testing include decrease cost of providing biomarker testing, decreased turnaround time on testing, and local provider input into the test menu. Some of the things that we considered when deciding to insource NGS was the cost to perform NGS testing versus sending it out, volume of specimens to be tested, expertise required, facility requirements, ease of workflow, did available panels meet our clinician and guideline needs, and if there was a comprehensive pipeline available from the vendor. We found a solution that fit our needs in all of these buckets.

After determining that insourcing NGS was the right thing to do for our health system we had to secure funding for the project. We prepared a business case using reference laboratory cost avoidance. This is an example business case for a NGS project:

  • Imagine that you currently send out 200 NGS tests per year for the same panel.
  • This reference lab NGS panel costs $3500 per sample.
  • You calculate that by insourcing the testing you can perform the test for $600 per sample (fully loaded with tech time, repeat rate, control cost, validation cost, QA cost, overhead).
  • This would save the health system $580,000 per year [($3500-$600)X(200 tests)].
  • Pretend the instrumentation required to perform the test in house cost $300,000.

Even the first year, the project could save the health system $280,000 ($580,000-$300,000). Subsequent years would be even more favorable. Showing a favorable return on investment (usually within a 5 year time period) would make it easy for the C-suite to approve insourcing this project.

Obviously money is not the only deciding factor when insourcing testing. I have to be able to perform a test cheaper, faster, and at least as well as the reference laboratory if not better or I will not insource a test.

There are a variety of reasons that you may not want to insource NGS testing. You may not have the expertise, facility, or volume for it to make sense to insource the testing. Are you stuck paying whatever your reference lab is charging you because you can’t in source the test? No.

If you have not negotiated the pricing and billing structure of your molecular pathology reference lab recently, it may be time to take a look around. Here are a few things to consider getting better pricing on send out testing:

  • Renegotiate. You can try to renegotiate with your current reference lab to decrease your contracted price.
  • Shop around. The molecular pathology lab market is growing. With competition comes better pricing.
  • Increase volume. You could try to standardize which lab your physicians are using to increase the volume to your reference lab. Most reference lab contracts are negotiated based on volume. So if you can increase the volume, it is likely that you can decrease the price you’re paying.
  • Direct billing. It is worth addressing who is billing the patient (and who has the highest risk of being stuck with the bill if the testing is not covered). Many molecular pathology labs now directly bill the patient (as long as the patient was not an inpatient within the last 14 days). You may want to explore this option when negotiating contracts.
  • Insurance coverage. You should also consider whether the test offered by the lab is approved for coverage by your most common payers.
  • Out of pocket costs. Many labs now have maximum out of pocket costs to patients that are reasonable. This ensures your patients are stuck with large bills.  

Whether you decide to insource or continue to outsource NGS testing, there are options that could decrease the cost and turnaround time for biomarker testing.

-Tabetha Sundin, PhD, HCLD (ABB), MB (ASCP)CM,  has over 10 years of laboratory experience in clinical molecular diagnostics including oncology, genetics, and infectious diseases. She is the Scientific Director of Molecular Diagnostics and Serology at Sentara Healthcare. Dr. Sundin holds appointments as Adjunct Associate Professor at Old Dominion University and Assistant Professor at Eastern Virginia Medical School and is involved with numerous efforts to support the molecular diagnostics field. 

Pieces of PCR Products

Molecular diagnostics tests come in many forms, but one of the simplest assays is a fragment based assay. The principle of such an assay is to perform polymerase chain reaction (PCR) on a segment of DNA. If there is a mutation, the PCR fragments will be different in size. Notably, this method is good for detecting mutations that cause the insertion or deletion of multiple nucleotides. This type of assay is not suitable for single base pair changes or small insertion/ deletions.

The fragment size is analyzed by labeling the PCR products with a fluorescent dye and then running them through a Sanger capillary sequencer. The fragments will be separated based on size and ideally give clean peaks with low background (Figure 1).

Figure 1. Sample fragment analysis plot (x-axis is time, y-axis is fluorescence intensity) with smaller fragments coming off earlier (more to the left on x-axis). Red peaks represent the molecular size ladder for calibration. Other colors represent fragments labeled with other fluorophores. The ladder also helps you ensure that fragments of different lengths are coming off of the analyzer at similar levels.

One common application of this assay type is to detect FLT3 internal tandem duplications (ITD). FLT3, Fms Related Tyrosine Kinase 3, is a tyrosine kinase growth factor receptor for FTL3-ligand, and regulates hematopoiesis. Mutations in FLT3 are found in 1/3 of Acute Myeloid Leukemia cases and confer a worse prognosis. FLT3 mutations lead to ligand-independent activation by either disrupting the auto-ihibitory loop of the juxtamembraneous domain through an ITD mutation or by an activating point mutation in the tyrosine kinase domain (TKD) (Figure 2).  

Figure 2. Mechanisms of FLT3 activating mutations through internal tandem duplication (ITD) in the juxtamembraneous domain or activating point mutations in the tyrosine kinase domain (TKD).

The type of FLT3 mutation is also important as there are tyrosine kinase inhibitors (TKI’s) that are being investigated for use in FTL3+ cases. Type I inhibitors bind FLT3 in the active conformation either in the ATP binding pocket or at the activation loop; these inhibitors are useful for both ITD and TKD mutations. However, Type II inhibitors bind inactive FLT3 near the ATP binding domain, so they affect ITD but not TKD mutations.As the site of ITDs is consistently in exons 14 and 15 of FLT3, primers flanking this region were designed to detect any mutations in this area (Figure 3). As some artifacts can arise from the PCR process and create false positive peaks, a green primer labels PCR products from one direction and a blue primer labels PCR fragments from the other direction, therefore enhancing specificity (Figure 4). A wild type (WT) sequence will thus be 327bp in either direction.

Figure 3. Depicted is a representation of the FLT3 JM region and the activating loop of the kinase domain. Green and blue dots with black arrows represent the relative positions of primers that target the JM region for ITD and yellow dots with black arrows represent the relative positions of the primers that target TKD mutations in the activating loop of the kinase domain. The yellow box has vertical black lines that represent the position of the wild-type EcoRV restriction digest sites. Image adapted from InVivoScribe.
Figure 4. A FLT3-ITD positive case is shown on the top with a longer segment present with both green and blue peaks present confirming a larger PCR product size. This mutation is present in only minority of cells that represent the aberrant AML population. Image adapted from InVivoScribe.

As mentioned previously, fragment analysis is not suited to detecting point mutations as would be found for TKDs. However, the FLT3 assay has overcome this issue. Investigators determined that the TKD point mutation at codon D835 disrupts the endonuclease recognition site of the enzyme ecoRV (Figure 3). Customized primers again produce a unique PCR fragment (149bp long), which when digested with ecoRV will produce a 79bp fragment in wild type FLT3. If a FLT3-TKD mutation is present the ecoRV will not cleave the fragment at this location, but another ecoRV cleavage site (right side of yellow box) will create a 127bp fragment (Figure 5). Without this second cleavage site, an enzyme failure could be interpreted as a mutation. Thus, the enzyme, ecoRV, must be active and only functional at a single site to produce a TKD mutation.

Figure 5. Panels representing PCR fragments that are undigested by ecoRV (top), digested and have a TKD mutation present (middle) and no TKD mutation detected (bottom). Image adapted from InVivoScribe.

References

  1. Daver Naval, Schlenk RF, Russell NH, and Levis MJ. Targeting FLT3 mutations in AML: review of current knowledge and evidence. Leukemia 2019; 33:299-312.
  2. https://invivoscribe.com/products/companion-diagnostics-cdx/. Last accessed December 8th, 2019.
  3. Pawar R, Bali OPS, Malhotra BK, Lamba G. Recent advances and novel agents for FLT3 mutated acute myeloid leukemia. Stem Cell Invest. 2014; 1(3). doi: 10.3978/j.issn.2306-9759.2014.03.03

-Jeff SoRelle, MD is a Chief Resident of Pathology at the University of Texas Southwestern Medical Center in Dallas, TX. His clinical research interests include understanding how the lab intersects with transgender healthcare and improving genetic variant interpretation.

The X-games of PCR

This is not your Mom’s PCR. These new kids on the block are making PCR extremely fast. PCR (Polymerase Chain Reaction) technology won the Nobel Prize for allowing molecular research to advance much more rapidly (for an interesting read on the quirky Laureate who gave up science to go surfing, read more here: Wikipedia ). It has become the most commonly used work horse of most molecular diagnostic assays, usually in the form of real-time PCR. It is used for a variety of purposes from detecting bacteria and viruses, identity testing for forensics and bone marrow engraftment, cancer mutation analysis, and even sequencing by synthesis used by Illumina for massively parallel sequencing.

This technique is still limited by requiring highly trained technologists to perform DNA extraction, time-consuming processing, and the time of real-time PCR itself. Overall, this process takes about a 5-8 hours. While this is much faster than in the past, it would be unacceptable for use in the point-of-care (POC).

But why would DNA testing need to be POC? The term sounds like an oxymoron in a field where many results have a 2-month turnaround time. There are certain circumstances where molecular testing would impact patient care. For instance, a doctor testing a patient in their office for a sexually transmitted infection would want to know if they have gonorrhea/ chlamydia so they could prescribe proper antibiotics. Similarly, POC molecular testing could be applied in a bioterrorism incident to test samples for an infectious agent. Or POC testing would benefit low-resource areas internationally where HIV testing could be used to manage anti-retroviral therapy in patients many miles from a laboratory.

For PCR as a test to be useful at the POC setting, it would have to provide a result within 10-15 minutes and be performed as a waived test. Two recent examples the demonstrate how this is possible have been highlighted at recent conferences of the American Association of Clinical Chemistry, which I just got back from: Extreme PCR1 and Laser-PCR.2

Extreme PCR refers to a technique of rapidly cycling the temperature of PCR reactions. The reaction occurs in a thin slide that evenly distributes the reagents, temperature and is clear to permit easy reading of fluorescence measurements (Figure 1). DNA Polymerase enzyme and primers to amplify the target DNA are added at much higher concentrations than normal (20x).

Figure 1. Thin reaction chamber for ultra-fast PCR.

This flies in the face of traditional PCR chemistry dogma as specificity would plummet and normal DNA could be amplified instead of target DNA. This would create a false positive. However, let’s think about what is actually happening with non-specific reactions. Primers are designed to match one region of DNA, which is very unique within the whole genome. However, the genome is so large that some segment may look very similar and be different in just 1 or 2 of the 20 base pairs that a primer matches. A primer could bind to this alternate region but less efficiently. So, the binding would be weaker and take more time to occur.

Therefore, by speeding up the cycling time to just a few seconds, only the most specific interactions can take place and non-specific binding is offset (Figure 2)!

Figure 2. Fluorescence from a dye that fluoresces when bound to double stranded DNA, which is increasing here within seconds (high point represents when the reaction temperature cools and dsDNA anneals, then low points represent heating to high temperatures).

Laser PCR does not report the use of increased reagents like Extreme PCR (it may be proprietary), but they boast a very innovative method to quickly heat and cool PCR reactions. GNA Biosciences use gold nanoparticles with many DNA adapters attached (Watch the video below for a great visual explanation!).

These adapters are short sequences of DNA that bring the target DNA and primers together to amplify the target DNA sequence. Then as the name implies, a laser zaps the gold beads and heats them up in a very localized area that releases the DNA strands. The released DNA binds another gold particle, replicates, rinses, and repeats. The laser energy thus heats the gold in a small area that allows for quick heating and cooling within a matter of seconds.

These new PCR methods are very interesting and can have a big impact on changing how molecular pathology advances are brought to the patient. On a scientific note, I hope you found them as fascinating as I did!

References

  1. Myrick JT, Pryor RJ, Palais RA, Ison SJ, Sanford L, Dwight ZL, et al. Integrated extreme real-time PCR and high-speed melting analysis in 52 to 87 seconds. Clin Chem 2019;65:263–71.
  2. CLN Stat. A Celebration of Innovation. AACC’s first disruptive technology award to recognize three breakthrough diagnostics. https://www.aacc.org/publications/cln/cln-stat/2018/july/10/a-celebration-of-innovation
  3. G. Mike Makrigiorgos. Extreme PCR Meets High-Speed Melting: A Step Closer to Molecular Diagnostics “While You Wait” Clin Chem 2019.

-Jeff SoRelle, MD is a Chief Resident of Pathology at the University of Texas Southwestern Medical Center in Dallas, TX. His clinical research interests include understanding how the lab intersects with transgender healthcare and improving genetic variant interpretation.