a pregnancy test or a rapid strep test, with results available in minutes.
What about accuracy? The reported rate of false negative results is as high as 50%, which is why antigen tests are not favored by the FDA as a single test for active infection.
However, the FDA recently provided emergency use authorization for a more accurate antigen test.
Because antigen testing is quicker, less expensive, and requires less complex technology to perform than molecular testing, some experts recommend repeated antigen testing as a reasonable strategy.
According to one test manufacturer, the false positive rate of antigen testing is near zero. So, the recent experience of Ohio Governor Mike DeWine, who apparently had a false-positive result from an antigen test, is rare.
Antibody tests (also called serologic testing)
How is it done? A sample of blood is taken.
Where can you get these tests? At a doctor’s office, blood testing lab, or hospital.
What does the test look for? These blood tests identify antibodies that the body’s immune system has produced in response to the infection. While a serologic test cannot tell you if you have an infection now, it can accurately identify past infection.
How long does it take to get results? Results are usually available within a few days.
What about accuracy? Having an antibody test too early can lead to false-negative results. That’s because it takes a week or two after infection for your immune system to produce antibodies. The reported rate of false negatives is 20%. However, the range of false negatives is from 0% to 30% depending on the study and when in the course of infection the test is performed.
Research suggests antibody levels may wane over just a few months. And while a positive antibody test proves you’ve been exposed to the virus, it’s not yet known whether such results indicate a lack of contagiousness or long-lasting, protective immunity.
The bottom line is: the true accuracy of tests for COVID-19 is uncertain.
Unfortunately, it’s not clear exactly how accurate any of these tests are. There are several reasons for this:
We don’t have precise measures of accuracy for these tests — just some commonly quoted figures for false negatives or false positives, such as those reported above. False-negative tests provide false reassurance and could lead to delayed treatment and relaxed restrictions despite being contagious. False positives, which are much less likely, can cause unwarranted anxiety and require people to quarantine unnecessarily.
How carefully a specimen is collected and stored may affect accuracy.
None of these tests is officially approved by the FDA. They are available because the FDA has granted their makers emergency use authorization. And that means the usual rigorous testing and vetting has not happened, and accuracy results have not been widely published.
A large and growing number of laboratories and companies offer these tests, so accuracy may vary. At the date of this posting, more than 170 molecular tests, two antigen tests, and 37 antibody tests are available.
All of these tests are new because the virus is new. Without a long track record, assessments of accuracy can only be approximate.
We don’t have a definitive “gold standard” test with which to compare them.