CDC Says COVID-19 Antibody Tests Could Be Wrong Up to Half the Time

Antibody tests for COVID-19 could be inaccurate up to half the time, per the Centers for Disease Control and Prevention (CDC).

The agency, as spotted by CNN on Tuesday, makes note of this in a new guidance message posted to the Interim Guidelines for COVID-19 Antibody Testing section of its official site. The CDC—following similar cautionary assessments from various health officials—state that antibody tests, also referred to as serologic tests, should “not be used to make decisions” regarding the grouping of people in congregate settings, i.e. schools, dorms, etc. Furthermore, these tests should not be utilized as part of efforts to get people back in traditional workplaces.

“In the current pandemic, maximizing specificity and thus positive predictive value in a serologic algorithm is preferred in most instances, since the overall prevalence of antibodies in most populations is likely low,” the CDC says. “For example, in a population where the prevalence is 5 percent, a test with 90 percent sensitivity and 95 percent specificity will yield a positive predictive value of 49 percent. In other words, less than half of those testing positive will truly have antibodies. Alternatively, the same test in a population with an antibody prevalence exceeding 52 percent will yield a positive predictive greater than 95 percent, meaning that less than one in 20 people testing positive will have a false positive test result.”