Lab Myths: Do You Know Why You Do Things?

Do you ever wonder how many of the things we commonly do in the lab are based on verifiable, objective data? A good way to discover the practices that I call lab myths is to teach laboratory medicine. Any student worth his or her salt will ask you why you perform tasks a certain way, and occasionally you will be unable to locate a good reason. Examples of this type of common practice abound and the following paragraphs mention a few.

Why do you wipe away the first drop of blood from a finger or heelstick for most uses? Everyone knows wiping away the first drop is the correct way to do a capillary collection, because the first drop of blood is contaminated with disinfectant and/or tissue fluid or tissue, etc. That only makes sense. Okay. My question for you is this: where’s the data that proves that? Has anyone ever actually analyzed the glucose, or sodium, or potassium, in the first drop, then the second drop, then the third drop and shown that there is a statistically different result, enough that you should not use the first drop? Or is it a lab myth? We do it because it makes sense and we’ve done it for as long as anyone can remember and everyone does it, but I have been unable to locate any actual data to support the practice. (And if you ask a group of diabetics, most of them use the first drop!)

Here’s another example: Blood gas samples should be sent to the lab on ice to prevent sample degradation. This is another common lab practice that everyone “knows,” and with this one you can find supporting data in places. Yet there is also data to suggest that if the sample is to be analyzed within 30 minutes, ice is unnecessary. In addition, many of those early studies were done on blood gas samples collected in glass syringes. There is data to suggest that there are different dynamics in samples collected in plastic syringes (1). When was the last time you received a glass syringe in your laboratory? The last glass syringe I’ve seen was filled with Novocaine and coming at me at the dentist office.

A third lab myth: 60 – 70% of all medical decisions are based on laboratory test results (2). You can find this statistic quoted everywhere in laboratory medicine (Mayo, CAP, Modernising Pathology Services document on UK Department of Health website, IFCC, to name a few). I’ve always wondered where the data is that supports this assertion. Granted I agree that it makes intuitive sense that the majority of medical decisions are based on laboratory data, however, has anyone actually demonstrated it with supporting data? It also makes sense that 95% of all statistics are made up on the spot.

These lab myths are examples that illustrate a point. Sometimes what we “know” can cause us not to question things we should question, and investigations are not performed that should be performed. It’s a good idea to always question a long standing practice because, like in the blood gas example, conditions may have changed (Who still uses glass syringes?). So think about it. Do you have your own lab myths?

  1. Mahoney JJ, Harvey JA, Wong RJ, Van Kessel AL. Changes in oxygen measurement when whole blood is stored in iced plastic or glass syringes. Clin Chem 37(7):1244-48. 1991.
  2. Forsman RW. Why is laboratory an afterthought for managed care organizations? Clin Chem 42(5):813-16. 1996.

 

-Patti Jones PhD, DABCC, FACB, is the Clinical Director of the Chemistry and Metabolic Disease Laboratories at Children’s Medical Center in Dallas, TX and a Professor of Pathology at University of Texas Southwestern Medical Center in Dallas.

Pediatric Labs are Different

Why do I say pediatric labs are different? A blood test is a blood test, right? Of course it is, however there are a lot of aspects of operating a pediatric lab that really are different from the way operations run in a lab whose clientele is mainly adults.

Most people can think of the most obvious difference: age-related reference intervals. The concentration of various biomarkers in the body changes as an infant grows and develops into an adult. In some cases, there’s not a lot of change in the biomarker. A blood pH is pretty constant over the course of a person’s life, as are the electrolytes. The reference intervals for these may be broader in infancy, but in general they don’t change a lot. However some biomarkers change so drastically that normal levels in childhood would be considered pathological in an adult. Without reference intervals tied to age or developmental state, these tests are not able to be properly interpreted. Alkaline phosphatase during bone growth and steroid hormones during puberty are two good examples of this.

The things that people tend not to think about that cause a pediatric lab to be different are predominately all centered on issues with sample volume. Especially in infancy, children have limited blood volume for testing, and this fact affects nearly every operation in a pediatric laboratory.

Front end processing of samples is affected, as often more than 60% of the tubes arriving in the lab are microtubes, which hold 1 mL or less. These tubes may not be able to hold a barcode label, nor fit on an instrument robotic system. The sample must be aliquotted into tubes that will fit a system, or hand fed into an instrument, and often hand-programmed into the instrument. More manual steps results in more opportunities for human error. In addition, the amount of sample used by any given instrument for testing must be considered. That sample volume includes the actual volume necessary for analysis, plus the volume necessary to run HIL (hemolysis, icterus, and lipemia) indices and the instrument dead volume (the volume below which an instrument cannot pipet the sample). Instruments with large dead volumes will not be found in pediatric labs.

Small sample volumes also affect the ability of the lab to add-on tests to samples already in the lab, or rerun samples later to check results. There may be insufficient volume to run more tests or rerun tests, or the sample may have evaporated and be unacceptable for running additional analyses. A study done using a 5 mL serum sample and a 0.1 mL serum sample and allowing both to sit open to the air for 4 hours showed that the 5 mL serum sample had less than 10% difference between original test values and those run 4 hours later. The 0.1 mL sample had more than 50% difference in its values. In addition, with just enough sample to run a test one time, if a dilution needs to be made, it may not be possible.

Lastly, there are a few test menu differences in a pediatric laboratory. Tests commonly found in pediatric labs, but essentially never in predominately adult labs include things like testing for inborn errors of metabolism and sweat chloride testing for Cystic Fibrosis. Conversely, common tests in an adult lab that are not performed in a pediatric lab include serum protein electrophoresis, PSA and other tumor markers. Some tests are performed in both labs but for different indications. For example, AFP is used as a tumor marker for hepatocellular carcinoma in pediatrics instead of as a maternal prenatal screening tool like in an adult lab.

These are some of the ways in which pediatric lab medicine differs from adult lab medicine, and offers unique challenges in day to day operations.

 

-Patti Jones PhD, DABCC, FACB, is the Clinical Director of the Chemistry and Metabolic Disease Laboratories at Children’s Medical Center in Dallas, TX and a Professor of Pathology at University of Texas Southwestern Medical Center in Dallas.

Educating the Doctors

If you had a chance to spend one day with a group of fourth year medical students who had already been accepted into residency programs, and you had the goal of providing them with the information any beginning doctor needs to know about the laboratory, where would you begin and what would you teach them?

I had this opportunity recently. The director of a medical school boot camp for Fourth-year medical students (MS4) who would start residency in two months approached me, wanting to know if I’d like this opportunity. Of course, I jumped at the chance. The hardest thing was deciding what information to leave out, to essentially focus the short course on the minimum information related to the lab that a doctor should know when they begin their career. I can honestly say that the opportunity was educational for me also – it showed me exactly how little a graduating doctor knows about the lab! Now in its third iteration, we learn and add and subtract as we go.

We do a brief introduction and overview of general lab structure and then start with phlebotomy. Most doctors (and I’m going to exclude everyone who entered medical school after being a medical technologist) have no idea that the tube top color indicates the type of anticoagulant, and for instance that every purple top tube everywhere in the world has EDTA anticoagulant in it.  We also covered basic phlebotomy technique. Then we rotated them in groups through the various sections of the lab, allowing each section to educate the group on the some of the items they considered the most important features of that section. Some of the topics that were covered include:

Client services/accessioning: some tests utilize a whole blood sample (CBC, blood gases), many, many samples require spinning and aliquotting while maintaining sample identity. Hemolyis, lipemia and icterus interfere with tests.

Chemistry: batch vs random access testing, main chemistry analyzer vs manual testing, pre-analytical affects on test results; reference intervals

Hematology: why clotted tubes can’t be used, how white cell differentials are performed (mostly manual in pediatric institutions)

Microbiology: blood culture bottles in the instrument vs plating and identification; how susceptibility testing works; likelihood of a false positive on a positive flu test run in the summer

Blood banking: what a type and crossmatch includes; how various blood products should be transported; uncrossmatched blood availability

Each section is also instructed to encourage questions and interaction with the MS4s as they tick off main points.

This is an educational opportunity I wish I were granted for all MS4s everywhere. Each year we run this program we refine it as we learn what they most need to know, as well as what they don’t know and what we don’t know. It’s a wonderful learning process.

 

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-Patti Jones PhD, DABCC, FACB, is the Clinical Director of the Chemistry and Metabolic Disease Laboratories at Children’s Medical Center in Dallas, TX and a Professor of Pathology at University of Texas Southwestern Medical Center in Dallas.

 

 

Podcast: Answers to Your Ebola Preparedness Questions

The editors of Lab Medicine recently sat down with ASCP President Dr. Finn, Dr. Nancy Cornish from the Centers for Disease Control, and Dr. Lance Peterson from NorthShore HealthSystem to answer your questions about laboratory preparedness for a patient infected with Ebola Virus. You can listen to it here.

Laboratory and Hospital Ebola Response

Laboratories are currently scrambling to define and put into place procedures for dealing with processing and testing of samples from highly infectious patients. The CDC has guidelines for healthcare workers and for laboratories specifically (http://www.cdc.gov/vhf/ebola/hcp/index.html). They also are very willing to help. Because Dallas had actual cases of Ebola, our hospital in Dallas mounted a hospital-wide response, in which the CDC and Texas State and County Health Departments were involved early on and throughout. This blog post describes the plans we instituted.

It quickly became clear that we did not want to transport infectious material through the hospital if we could avoid it, keeping everything infectious isolated in a single area. The hospital cleared an ICU wing which contained two negative pressure rooms, and the laboratory used an ICU room two doors away to create a mini-lab. The entire ICU wing was closed off as an isolation zone. No samples will leave the isolation zone unless they are headed for the CDC or State lab, and those will be couriered directly from the isolation zone.

All testing that can be, will be done on the I-stat in the patient room, including electrolytes, BUN, creatinine, ionized calcium and blood gases. A meeting was held with the ICU physicians who will be treating patients, to ask what testing they could foresee requiring other than those available on the I-stat. Their final list included platelets, CBC and coag tests, and originally also asked for ammonia and liver function tests. The only test we could not provide for them was ammonia. We couldn’t find a way to perform ammonia on a whole blood sample and had decided not to centrifuge any samples due to the possible risks of aerosolizing the sample and additional risks associated with aliquotting samples.

For the coag tests, we chose to use the I-stat PT/INR. Knowing that PT/INR on the I-stat is not FDA approved for anything other than Coumadin monitoring, we performed a full CLIA validation of the PT/INR in order to be able to use it for Ebola patients. Using the I-stat this way causes the PT/INR to become a high-complexity test, therefore only those individuals with appropriate licensure, training and competency will be performing the test at bedside.

Testing other than what is available on the I-stat will be done in the mini-lab set up in the nearby ICU room. It will be performed by lab personnel in full PPE, including PAPR (powered air purifying respirators), 3 layers of gloves, etc, all within the isolation zone. Lab testing in the mini-lab will occur once a day, with a possibility of twice a day. We purchased an Abaxis Piccolo for performing the liver enzymes and a Sysmex pocH-100i for the CBC and platelets. Both these analyzers will be run in the mini-lab room. The piccolo will be run inside a biosafety cabinet (BSC) which was put in the room because the piccolo is not a closed system. Sample pipetting into the piccolo carousel will occur in the BSC.

As far as blood utilization, the plan is to perform a one time, ABO only, blood typing on admission of a patient. A blood bank technologist in full PPE will perform the ABO only blood type manually in the BSC in the mini-lab. This ABO only typing has also been validated on samples allowed to settle rather than being centrifuged. The plan is for any patients to receive type O-negative blood if transfusions are required. However if they should require type-specific blood products for any reason (i.e. shortage of O-negative), it was felt that performing the blood type early before viral titers are really high would be better than waiting.

To work in the isolation wing, personnel must don full isolation PPE, including PAPR, etc, with a multi-step system in place for both donning and doffing the equipment. A buddy system is used throughout, with training on all procedures being continuous. The lab personnel who have volunteered to staff the mini-lab have undergone the PPE training. All of this perhaps excessive care is being taken in order to protect all other patients, as well as all healthcare team members, both lab and non-lab. Although Ebola may never reach our hospital, we live in a world where global travel makes if very likely that we will see patients with this or other highly infectious diseases appear in our facilities. It’s important to be as prepared as possible.

 

-Patti Jones PhD, DABCC, FACB, is the Clinical Director of the Chemistry and Metabolic Disease Laboratories at Children’s Medical Center in Dallas, TX and a Professor of Pathology at University of Texas Southwestern Medical Center in Dallas.