Q&A :: ASK THE EXPERT Readers’ questions answered


the relative likelihood of a false positive result when compared to testing done on individuals with low pre-test probability. Second, in order to correctly interpret the


Charles K. Cooper, MD Chief Medical Offi cer


Siemens Healthcare Diagnostics,


Siemens Healthineers Q&A


An issue that comes up for me again and again are questions from primary care physicians about interpreting positive drug screens and reflex confirmatory testing. Is there a table or quick reference that would explain what metabolites are commonly seen in patients taking different (and sometimes multiple) pain formulations? Often a doctor is prescribing one drug, but suspects the patient is taking that and others. What substances can cause false positives in drug testing? Sometimes a physician contacts me when they tell the patient that their testing suggests additional drugs and the patient disagrees, perhaps suggesting that supplements or other medications might be responsible.


Any assistance would be appreciated.


Determining when to test for drugs of abuse (DOA), which test to use, and how to interpret test results is unavoidably complex and belies the simplicity of the reported results. Clinicians should be encouraged to become familiar with important aspects of testing for DOA as there are some basic concepts that can be helpful. First, become familiar with appro- priate indications for testing to maximize the clinical value of such testing and to reduce the chances of unintended conse- quence. Common testing scenarios include drug treatment programs, pain manage- ment programs, and psychiatric treatment. These scenarios involve patients with a higher pre-test probability, which reduces


48 DECEMBER 2022 MLO-ONLINE.COM


results of DOA testing, it is important to understand the limitations of DOA testing, which is most often conducted via highly sensitive laboratory immunoassays. For example, these tests do not definitively prove that active intoxication is present, since sensitive immunoassays may detect the presence of levels below that which are associated with intoxication. Also, there are a number of potential causes for false posi- tives that clinicians should become familiar with. When necessary, confirmation testing with chromatography or gas chromatogra- phy/mass spectrometry should be ordered to provide certainty, however, clinicians should be aware that such confirmation requires additional time as these methods are not as fast as automated immunoas- says. Also, point-of-care tests may not be as accurate as laboratory-based immunoas- say testing as numerous publications have demonstrated performance estimates that underperform labeled claims. Finally, false negative results are possible due to patient subversion techniques such as through the use of masking agents, attempts to dilute the urine via either ingestion or addition of water, addition of adulterants, and switch- ing urine specimens. Clinicians should be encouraged to


advance their knowledge of this topic to aid in test ordering and results interpretation. There are good resources available to clini- cians to advance their understanding such as a recent review article that appeared recently in the Am Fam Physician medi- cal journal (https://www.aafp.org/pubs/ afp/issues/2019/0101/p33.html) as well as a number of resources at the webpage of the National Institute on Drug Abuse (https:// nida.nih.gov/nidamed-medical-health-pro- fessionals/health-professions-education/ cmece-activities).


As a fully vaccinated, retired medical laboratory technologist, I have family and friends who question the need to be vaccinated against COVID-19. What are the best ways for persons like me to help counter their fears and advocate for the value of being vaccinated?


Many thanks for revival of a Q&A column in MLO!


It’s not altogether surprising that people may have grown weary about COVID-19 given the extremely stressful experience that societies around the world have expe- rienced in the past few years. However, we have to be careful not to allow pan- demic fatigue to inaccurately color the importance of vaccination. The data is conclusive that COVID-19 vaccination reduces likelihood of severe disease and bad outcomes particularly for those at increased risk. When one considers the fact that the currently circulating Omicron subvariants of SARS-CoV-2 are among the most contagious and transmissible viruses that humans encounter today, it is reasonable to view infection and/or exposure as a question of when not if. With this in mind, people need to decide how they will obtain their immunity, either via immunization or infection. Immunization, with several hundreds of millions of doses administered to date, has a well described safety profile with more predictable out- comes than what may be experienced with actual infection. People who are reluctant to obtain vaccination should be encouraged to become educated about the safety profile of vaccines as well as the risk factors associated with severe disease to help them make a more informed decision and to more effectively manage personal risk. The CDC has good resources to help people understand their risk, which can be found at this website: https://www.cdc. gov/coronavirus/2019-ncov/your-health/ understanding-risk.html.


I saw in your bio that you co- led the efforts to create the Quantitative Safety Division in the Center for Drug Evaluation and Research (CDER). Could you please explain what “quantitative safety” is?


Quantitative safety is a descriptor for a drug safety division that was created in CDER at FDA for the purpose of perform- ing advanced quantitative evaluation of drug safety signals utilizing techniques such as meta-analysis and Bayesian analysis. FDA receives large amounts of high-quality phase 3 clinical trials and is in a unique position to utilize this data for the purposes of answering important safety questions.

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