Accurate information surrounding COVID-19 testing builds trust with the public so they understand how and why certain tests are being conducted—whether those are rapid tests conducted at home or antibody tests that help researchers learn about the virus. The more testing, the more we know how to prevent further spread and health problems.
Not all testing is 100%. COVID tests of all types can yield incorrect results, whether the fault of the administrator, an insufficient sample size, or any number of mishaps. Though not widespread in scope, reports of false positives and false negatives can raise doubts about COVID testing accuracy, including with antibody tests. But what’s the full story? How accurate are COVID-19 antibody blood tests, specifically?
Antibodies detected in your blood during a serological test indicate you’ve been exposed to the virus—unless, of course, your test is a false positive. But some issues surround the COVID-19 antibody test because enough antibodies have to be present for the possibility of detection. A serological test is not useful, for example, to learn if someone is infected with COVID, because they may be early in the stages of infection and don’t have enough antibodies to be measured.
A COVID antibody test results normal range can vary as post-vaccine antibody levels and post-infection antibody levels vary widely. But an antibody test is reported as positive at an index of ≥0.8 U/mL, and a negative result is reported at an index6 of <0.8 U/mL.
A common question surrounding serological tests is: am I immune to COVID19 if my antibody test result is positive? While the antibodies detected in your blood mean you’ve previously been infected with COVID 19—and while reinfection is extremely rare—doctors still don’t have enough data to be able to confidently associate a positive antibody test with immunity.
Prior to vaccination, a positive COVID19 antibody result likely means that you were infected with COVID at some point, even if you didn’t show symptoms. In this case, it’s possible you were one of the more rare asymptomatic infected cases.
The Centers for Disease Control (CDC) advises that, in general, a positive antibody test indicates a person was previously infected with COVID19, but it does not indicate a current infection. The safest way to return to work with a positive result from a COVID19 antibody test is to also receive a antigen or molecular COVID 19 test, or to have been previously vaccinated.
While the CDC says reinfections can occur, the chances are low, especially if you show antibodies. If you are not showing symptoms, and have not been exposed to someone infected with the virus recently, you can likely go to work.
COVID19 antibodies form after a person has been infected—they are a response to the virus. While some antibodies can appear several days after initial infection, they aren’t typically in numbers large enough to be detected by a serological test until 10-20 days after infection. Again, this is why COVID19 antibody tests aren’t used to detect infection, but instead they are used to determine previous infection.
Similar to antigen and molecular COVID-19 tests (more so with antigen), false negatives and false positives can occur with serological tests—and sometimes for similar reasons. When there are too few antibodies present, a test can’t get an accurate reading—and we currently don’t have enough data about antibodies to know how long their levels sustain themselves.
False positives can occur when the serological test mistakes similar antibodies in your blood for those related to COVID-19. Because COVID-19 is a strain of coronavirus, your body can develop similar antibodies to other types of coronaviruses the test can mis-identify. False positives can also occur when the test quality was flawed due to user error or manufacturing.
Accurate testing is a critical need to combat COVID-19. At BioCollections Worldwide we understand the importance of accurate testing. Accurate testing helps us better understand viruses like coronavirus, their spread, and how to move towards immunization and control. And by honing in on accuracy, we can determine what tests are more prone to accurate results than others. Straightforward, affordable, fast testing—that’s our mission.
If you’re interested in a test, or just curious about how BioCollections works to provide the best in COVID-19 testing and research, contact us to learn more about how we can help. With over twenty years in the industry, and with multiple national and international locations, we were equipped with the experience to jump into action when COVID-19 became a worldwide problem, and we remain committed to continued testing.