ADVERTISING: Advertorial — DR. WENDY CUNNINGHAM: Antibody tests for COVID-19
Those of you who have been sick in recent months but did not get tested for COVID-19 have been left wondering whether you may have had the coronavirus. There are also those who did not get sick but may have been exposed to the virus (an asymptomatic infection). Antibody tests can be used by people in both groups to find out.
Antibodies are proteins made by the immune system to fight a virus. If you have a specific antibody in your blood, it means that you were exposed to that specific viral infection in the past. The timing of the blood test to check for antibodies is important. IgG antibodies are detectable 10-14 days after exposure to SARS-CoV-2. Antibody tests should not be used to diagnose someone who is currently sick with COVID-19. To see if you have a current infection, you need a viral test (NAA), which checks respiratory samples, such as a swab from inside your nose.
The latest FDA-approved antibody test is highly accurate, but most of the tests available have not been FDA-approved. New data is being collected every day to see which testing is most accurate. LabCorp has just released that their SARS CoV-2 IgG Antibody test, if tested 14 days or more after onset of symptoms, has a sensitivity of testing at 98.5-100% and specificity at 98.8-99.3% for the methods used in LabCorp labs nationally.
We are in changing and uncertain times as we navigate through the COVID-19 pandemic. If you test positive for COVID-19 antibodies, it means that you were exposed in the past and have developed the detected antibody. Unfortunately, there may be a false positive if a patient was exposed to another non-SARS-CoV-2 coronavirus strain. These non-SARS-CoV-2 strains are common and are one cause of the common cold. We do not have the numbers today on how often the false positives due to cross reactivity may occur.
Due to all these unknowns, a positive result does not prove that you are immune to COVID-19, or that you are not currently infected. It is unclear if those antibodies can provide immunity against getting infected again. This means that we do not currently know if these antibodies make you immune to the virus long term.
If you test negative for COVID-19 antibodies, you probably did not have a previous infection, or your antibody levels were too low for the test to detect. Since antibodies do not show up for 1 to 3 weeks after infection, it is possible you could still get sick from a recent exposure. Individuals who are immunosuppressed or who are on drugs that suppress the immune system may test negative despite being exposed to SARS-CoV-2.
CDC is looking at data from antibody tests to estimate the total number of people who have been infected with SARS-CoV-2 in the United States. CDC is also using antibody testing to learn more about how the body’s immune system responds to the virus and to explore how the virus spreads among people exposed to it.
Antibody tests are only available through health care providers and laboratories.
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For more information, contact Dr. Wendy Cunningham at email@example.com.