What is the purpose of COVID-19 antibody testing?
On an individual level, an antibody test looks for antibodies in the blood. Your immune system makes antibody proteins to help fight infections. If you were exposed to COVID-19, an antibody test will show whether or not you’ve developed antibodies against SARS-CoV-2, the virus that causes COVID-19. An antibody test cannot tell you whether you have a current COVID-19 infection.
On a population level, antibody testing can give researchers a sense of how many people have been exposed to and infected by COVID-19. In the future, antibody testing may show whether someone has immunity against COVID-19, meaning that they cannot get infected again. If antibodies make people immune to COVID-19, it can help inform leaders and public health officials about whether the population has reached herd immunity. Herd immunity is when a large percentage of a population has become immune to COVID-19, which can protect those people who are not immune.
What are the different types of antibodies? Do they offer different types of immunity?
There are three different types of antibodies: IgM, IgG, and IgA.
- Immunoglobulin M (IgM) is usually produced as the body’s first response to an infection. However, for COVID-19, IgM antibodies are produced around the same time as IgG antibodies. Generally, IgM may provide short-term protection and can help tell if an individual has been recently infected.
- Immunoglobulin G (IgG) is the most common type of antibody. It’s usually made several days to weeks after most infections. However, for COVID-19, IgG antibodies are produced around the same time as IgM antibodies. Generally, IgG remains in the body and may provide long-term protection against future exposure.
- Immunoglobulin A (IgA) is found in the blood, sinuses, lungs, and stomach. Generally, IgA helps protect these areas from infection. However, it’s unknown what role these antibodies play in determining exposure or immunity to COVID-19.
There is not enough evidence at this time to suggest that people who have these antibodies are protected against future COVID-19 infections. Additionally, antibody testing by itself should not be used to establish the presence or absence of COVID-19 infection or reinfection. Visit the CDC website for further information.
When do antibodies develop?
Based on the most current research, antibodies develop around 1 to 3 weeks after infection from COVID-19. However, this varies by individual, and some people may take a longer time to develop antibodies.
Do all COVID-19 antibody tests look for the same types of antibodies? Is there any advantage in getting one type of antibody test over another?
All COVID-19 antibody tests look for antibodies in the blood specific to the virus. There are antibody tests that look for one specific antibody (such as an IgG test). Other antibody tests look for the presence of multiple antibodies (such as a total antibody test). Both types of tests are helpful when trying to check if you have been exposed to the virus. At this time there is no advantage in checking for one antibody versus another. IgM and IgG antibodies are most useful when checking for past exposure to COVID-19. The CDC does not recommend testing for IgA antibodies.
Can antibody tests be used to diagnose a COVID-19 infection?
Antibody tests do not show whether a person is currently infected. A molecular (PCR) test is a more reliable indicator of current COVID-19 infection.
Antibody testing by itself should not be used to establish the presence or absence of COVID-19 infection or reinfection. Individuals might get tested too early before antibodies develop, and some individuals never develop detectable antibodies following infection. Additionally, having antibodies may indicate a previous infection and may be unrelated to the current illness.
Can I use a semi-quantitative COVID-19 antibody test to determine my level of immunity?
A semi-quantitative antibody test can help identify individuals who have developed an immune response after exposure to COVID-19 or vaccination. However, it should not be used to determine the level of immunity you have. However, evidence is still being collected to determine if antibodies provide protective immunity against SARS-CoV-2 (COVID-19) specifically. Follow up with your healthcare provider for additional guidance on how to interpret your test results.
Can I use a semi-quantitative COVID-19 antibody test to track my antibody levels over time?
This test provides a numerical value that helps determine whether or not you have antibodies at the time of testing. However, it is still unknown whether or not it is useful to track antibody levels over time. Follow up with your healthcare provider for additional guidance on how to interpret your test results.
My COVID-19 antibody test was positive, but I’m still having symptoms. What should I do?
If you’re having symptoms of COVID-19, contact your healthcare provider or local health department to get tested for active infection. The antibody test can only tell you if you’ve been exposed and have developed an immune response, but it cannot say whether you have an active infection.
My COVID-19 antibody test was negative, but I previously tested positive for COVID-19 or was exposed. Is my result incorrect?
Getting an antibody test too soon after being infected may cause a false negative result. It usually takes around 1 to 3 weeks after being infected with COVID-19 for your body to produce enough antibodies to be detected in the blood. However, current research shows it may be best to wait 3 to 4 weeks after infection to get tested for antibodies. Some people may take even longer to develop antibodies or may not develop enough antibodies to be detected by the test. It is recommended that you contact your healthcare provider or local health department to see if retesting is needed.
If my COVID-19 antibody test is positive, can I get sick again with COVID-19?
If your test results show that you’re positive for COVID-19 antibodies in the blood, it means you’ve likely been exposed to COVID-19. Although having antibodies usually gives immunity from further infection, there is not enough evidence at this time to suggest that people who have these antibodies are protected against future COVID-19 infections.
What is the chance that my COVID-19 antibody test result was a false positive?
False positives occur when a person tests positive even though they DO NOT have the antibodies for COVID-19. There is a small chance that the result could be a false positive. Manufacturers must demonstrate a high specificity of approximately 99% to 100% to ensure validation of their test. If you have additional questions, please contact the lab directly for more information.
If I had more severe symptoms of COVID-19, will I have a higher antibody level?
Some studies have shown that individuals with more severe symptoms develop higher antibody levels. However, although having antibodies usually gives immunity from future infection, there is not enough evidence at this time to suggest that people who have higher amounts of these antibodies are better protected against future COVID-19 infections.
Can I have antibodies if I did not have any symptoms of COVID-19?
You can have antibodies from an asymptomatic COVID-19 infection. An asymptomatic infection is when you are infected but do not show any symptoms.
Can my antibody value change over time?
It usually takes 1 to 3 weeks for antibodies to be detected in your blood. Because antibodies develop over time, it’s possible that your antibody levels can change depending on when you tested.
My antibody value is low. Should I get retested to see if my result will change?
It usually takes 1 to 3 weeks for antibodies to be detected in your blood. Because antibodies develop over time, it’s possible that your antibody levels can change depending on when you tested. However, this varies by individual. Talk with your healthcare provider or local health department about your results to see if retesting is advised.
What does an indeterminate COVID-19 antibody test result mean?
If your test result is indeterminate for COVID-19 antibodies in the blood, this means that the results were neither positive nor negative. You will likely need to be retested in order to confirm whether or not you have antibodies in the blood. An indeterminate result can happen if you do not have enough antibodies in your blood for the test to detect, such as if you test too soon after becoming infected. This result can also happen if there was a problem with your sample or the test itself.
Based on the results of my antibody test, do I need to continue social distancing and/or wearing a mask? Can I visit someone who is at risk for severe symptoms of the virus?
At this time, there is no test that can tell you when to stop social distancing or isolating. Be sure to check with your healthcare provider about next steps and continue to follow federal, state, and local government guidance regarding social distancing and COVID-19 safety precautions. You should also use caution or avoid visiting at-risk individuals like those above the age of 65 or with pre-existing medical conditions.
If I have antibodies, am I a good candidate for donating plasma?
People who have fully recovered from COVID-19 and have antibodies are encouraged to consider donating plasma. You must be completely recovered from symptoms for at least 14 days prior to donation. If you have additional questions, please contact the donation center directly for more information.