Your COVID-19 Questions & Answers
Response from Tom Belhorn
Q:
I know the COVID serology tests have been mentioned before and are now available at UNC. Can anyone order this test? Are these tests accurate? Do these tests have any role in diagnosis?
A:
There are currently >100 different COVID serologic assays being marketed in the US. Many are inaccurate. UNC lab personnel tested several assays following FDA guidance, and chose the Abbott COVID-19 IgG test that now has EUA (Emergency Use Authorization). In testing UNC samples (including COVID-positive sera and patient sera from non-COVID-19 coronaviruses), no cross-reactivity was detected (with endemic coronaviruses) with this test. The experience so far reveals an excellent specificity, but no test is 100%. Even with a test with high sensitivity and specificity, if the seroprevalence is low (as is likely the case in NC), the positive predictive value is not that high (i.e., you can have quite a few false positives!). Currently you can order this test on any patient. Just take care how you interpret results. IgG often becomes positive more than a week into the illness and this is variable. And as stated before, with information available now, a positive COVID-19 IgG does not confirm immunity and does not mean you are virus-free (non-infectious). The antibody testing is most helpful now in providing information on epidemiology. With further data, though, results will likely be useful for providing patient-specific diagnostic information with greater certainty.