Politicians tell us that we need more COVID testing, that more testing is the key to getting rid of the novel coronavirus. But now, CNN publishes an article, “Antibody tests for Covid-19 wrong up to half the time, CDC says.”
I wonder what average people think when (and if) they read headlines like this one. Do they think that tests don’t work? Or do they just ignore the story altogether? After all, there have been so many contradictory messages. “Masks don’t work” became “you have to wear masks” virtually overnight. “Coronavirus stays on surfaces for days” became “coronavirus not easily spread on surfaces.” We were told that there could be no assemblies of more than a few people. New York Mayor De Blasio banned the St. Patrick’s Day parade and kept beaches closed, yet permitted protest rallies, marches and rioting.
Appropriate use of testing is a complicated issue. Any practicing doctor will agree. It is hard to explain to patients why tumor markers are not good screening tests, why we don’t do annual screening CT scans. It is hard for medical students to understand also. I vividly remember the Med School Professor who literally had a heart attack when students became belligerent because they couldn’t comprehend Bayes’ theorem. The professor walked off the stage clutching his left shoulder. Even with many experienced doctors, discussions of sensitivity, specificity and predictive positive value of tests make their eyes glaze over, though good doctors understand the limits of testing intuitively.
In my neighborhood, many patients want to get an annual Lyme test because they walk in the woods. I ask if they have had symptoms of either acute or late Lyme disease. Then, I explain the reasons testing is not indicated according to UpToDate.com:
Serologic testing for Lyme disease should not be performed:
●For screening of asymptomatic patients who live in endemic areas
●For evaluation of patients who present only with nonspecific symptoms (eg, fatigue, myalgias/arthralgias)
We do not test these patients, since the use of serologic testing in populations with a low pre-test probability of Lyme disease results in a greater likelihood of false-positive test results than true-positive test results. As a consequence, asymptomatic patients and those with nonspecific articular or neurologic symptoms may be incorrectly diagnosed as having “chronic Lyme disease” and receive unnecessary antibiotics.
Invariably, at the end of this discussion, the patient looks upset and I say “OK, we’ll do a Lyme test.”
It is the same with SARS-COV-2 antibody testing. Those without symptoms of real influenza-like illness since March have a low pre-test probability of disease, even in New York. Yet, everybody and their brother wants an antibody test. The TV blares out that the County is giving free antibody testing to first responders like they are handing out medals. Really, the government is just collecting population data rather than doing something that benefits the individual. The rest of the people infer that these tests must be important (the news media tout them endlessly) and go to doctors to get the tests. Urgent care clinics promote the tests because it is a new revenue stream. Employers are interested in getting their employees tested because the Governor said it is needed, though neither can explain what an employer would do differently if the tests are positive. In fact New York Governor Cuomo was so adamant about antibody testing, he demanded President Trump force industry to make more antibody tests. “We have 9 million people we want to get back to work,” Cuomo said during his daily briefing at the Capitol.
Newsflash. No one needs an antibody test to go back to work. Employers would be better served by consulting Occupational Medicine physicians rather than being mandated to follow orders of politicians whose grasp of medical science is tenuous at best.