The CDC recently modified its COVID-19 testing recommendations, guiding people to get screened after possible exposure regardless of whether they have any symptoms of the virus. And now the president and first lady have tested positive with likely many more in their circle to follow. So are the tests accurate enough to trust?
The CDC lists two types of tests people might take if they want to confirm COVID-19, but doctors are most likely to order a viral test if they’re looking for an active infection. To perform this test, techs take samples of mucus, usually from nasal or oral swabs, and add samples of specific antigens that have been shown to react to the virus’ presence. Don't worry, the days of "brain-tickling" are in the past as testing has adapted and changed. If the sample reacts to the antigens, the person likely has COVID-19. The viral test is the only test recommended by the CDC.
One problem with viral tests is their varying reliability. The rate of false-negative results averages about 10%, although some tests can have shown false-negative rates as high as 15%. The resulting sense of security some people are getting from these results could be dangerous. Sick people who believe they’re clear of the virus might be less cautious around others in their social bubbles, which could lead to increased disease spread.
People curious about the possibility of a recent COVID-19 infection might get an antibody test. These tests look for the presence of certain antibodies that are usually present when a person is fighting or has fought, an infection. The two antibodies doctors typically test for are called IgM and IgG.
Typically, the immune system starts sending out IgM antibodies within the first few weeks of infection. Merck Manuals explains that these antibodies typically increase in numbers for several weeks, and then they drop off when IgG, longer-lasting antibodies, begin to rise. Testing for both IgM and IgG usually lengthens the window for disease testing.
SARS-CoV-2, the virus that causes COVID-19, causes an unusual immune response: Both IgM and IgG appear to rise and fall concurrently, usually appearing between 1 and 3 weeks into the infection. Experts still aren’t sure how long the antibody levels remain once they show, but blood tests usually come back positive either for both or neither.
If they both follow the typical pattern for IgM antibodies, then antibody tests for COVID-19 are likely to come back negative within a few months of disease onset, no matter what. This test also has a high potential for false-positives due to cross-reactivity with other coronaviruses, like the ones that cause common colds. All in all, this test is so unreliable for COVID-19 testing that the CDC is unwilling to back its use for this purpose.
Those of us wanting to know where we stand with COVID-19 might not have access to solid answers, and our options could remain just as limited. Most people will receive accurate results, but not everyone will be so lucky. Until the false-negative rate gets addressed, we could have far too many people living with a false sense of security, continuing to spread the infection so remember that even if you tested negative, you may still infect others, and should still mask up.
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