Last month I blogged about key points to consider when preparing to do lab testing in the field. Here I will expand on using point of care testing in medical missions. Point of care testing is easy to use and relatively easy to access, making it very attractive for use in the field or on medical missions. In fact, it is tempting to take these tests and go rogue – it’s not uncommon for point of care diagnostics to be obtained by non-laboratory professionals and tossed in luggage to be used by short-term medical teams. However, this is not in the best interest of the patients or the community. Helping establish point of care testing for medical missions is one very important way that a laboratory professional can get involved in this kind of outreach.
Proper utilization and quality assurance practices are just as critical in the outreach situation as at home in a large lab. Perhaps even more so; for example, in areas with high disease prevalence, false positives and negatives can significantly affect patient care and population health. Under-diagnosis due to false negatives means that those who need treatment might not get it, just as over-diagnosis due to false positives may cause patients to get unnecessary treatment. Unnecessary treatment, especially for infectious diseases, harms the community by contributing to drug resistance.
Most point of care tests, especially lateral flow tests, have built-in controls which lessens the need to run QCs with patient testing. However, it is important to know the limitations of the testing. Sometimes point of care testing systems that are not available in the United States are selected for use in outreach in foreign countries. It’s more likely that an American medical team would be unfamiliar with the tests. A laboratory professional can help establish or at least verify the validity of the tests, including limits of detection and accuracy, before they are deployed. Also, it is often helpful to have the results interpreted for the end user. Little interpretation is needed for the more straightforward qualitative tests that simply give a positive or negative result. Even with these tests, the limit of detection should be available to the provider, especially if this is significantly different from that which the provider is accustomed. Tests that involve titration, such as some of the rapid typhoid and syphilis testing, benefit from having an explanation of what the titers mean clinically available to the end user.
Other tests with results that are prone to confusion are point of care versions of assays more commonly performed in clinical laboratories. Difference in reference intervals for the POCT compared to a conventional test can be particularly confusing. For example, the results of a lateral flow point of care C-reactive protein assay have a different reference interval than results from high-sensitivity C-reactive protein assays used in clinical labs. Using the incorrect reference interval to determine whether a result is normal can lead to over- or under-treatment, which is contrary to the purpose of diagnostic testing. Yet, when using point of care tests in the field, there is not a neat little interpretive comment accompanying the result.
So, how can this be remedied? If the laboratory professional is also on the team, they can be available to provide information as needed. However, if the team is not so fortunate as to have their own laboratory professional, another way to provide the information is to provide a short guide to cheat sheet that briefly explains how to use test results.
Proper utility is also important, especially in areas with high burden of disease or in areas where there is no confirmatory testing. Consider rapid tests for H. pylori. These typically detect antibody to H. pylori, which can be found in up to 70% of asymptomatic populations. The rapid test is of little utility since positive results only indicate the presence of antibody and not necessarily an active infection. Consider using rapid screening tests, such as for HIV, when confirmatory testing is not available. Sometimes a second screening test that employs a different method than the first can be used as a confirmatory test if nothing else is available.
Consider environmental limitations of the testing when selecting tests for use in the field. Many tests are unreliable at extremes of temperature and humidity. This might not always be obvious even when quality controls are used properly. For example, Tang et al (1) showed that the effect of temperatures and humidity similar to what was experienced in Louisiana after Hurricane Katrina on quality control material for a POCT glucose meter system caused significantly depressed results. Also keep in mind that exposure to environmental extremes can reduce the shelf life of POCT and related reagents. If using POCT long term, it is good practice to routinely test a known standard – even on tests with built in quality controls such as the test line on lateral flow tests – to ensure there has not been degradation in quality due to the environment.
Preparing POCT for medical missions is a great way for a laboratory professional to get involved in global health and outreach. From helping to select appropriate tests, to verifying test validity, to teaching proper utilization of testing and providing interpretive guideline, the laboratory professional is a vital part of a medical mission – even if they never leave their lab!
- Tang CS, Ferguson WJ, Louie RF, Vy JH, Sumner SL, Kost GJ. Ensuring quality control of point-of-care technologies: effects of dynamic temperature and humidity stresses on glucose quality control solutions. Point of Care 2012;11:147-51.
–Sarah Riley, PhD, DABCC, is an Assistant Professor of Pediatrics and Pathology and Immunology at Washington University in St. Louis School of Medicine. She is passionate about bringing the lab out of the basement and into the forefront of global health.