What causes false negatives in COVID-19 antibody tests?

Having an antibody test too early can lead to false negative results. That’s because it takes a week or two after infection for your immune system to produce antibodies. The reported rate of false negatives is 20\%.

Are antibody tests used to diagnose COVID-19?

No. An antibody test does not detect the presence of the SARS-CoV-2 virus to diagnose COVID-19.These tests can return a negative test result even in infected patients (for example, if antibodies have not yet developed in response to the virus) or may generate false positive results (for example, if antibodies to another coronavirus type are detected), so they should not be used to evaluate if you are currently infected or contagious (ability to infect other people).

Can COVID-19 antibody test detect current infection?

• Antibody tests should generally not be used to diagnose a current infection with the virus that causes COVID-19. An antibody test may not show if you have a current infection because it can take 1 to 3 weeks after the infection for your body to make antibodies.

What happens if my HIV test is negative after 6 weeks?

With antibody-only tests (3rd generation) only 0.3\% of tests (3 tests in every 1000) will be a false negative after 3 months. With 4th generation tests this is even lower. In practice, a negative result after six weeks means you do not have HIV. You do not need to test again unless you have new risks in the future.

Can a 4th generation test be negative after 6 weeks?

A 4th generation test that is negative after six weeks does not need to be confirmed. Is a negative test 100\% accurate? HIV tests after the 3 month window are more than 99.97\% accurate. They work for all types and subtypes of HIV. Very few medical tests have 100\% accuracy.

Can someone be HIV positive and not know it?

There will still be rare cases where someone is HIV positive and not picked up. However, HIV tests are one of the more accurate tests for any medical infection. Tests showing a negative result are ‘interpreted’ as negative. If the result is negative three months after exposure your result is interpreted as negative.

How soon after an exposure to HIV can I get tested?

To learn more about the window period and when a person should get retested, see CDC’s How soon after an exposure to HIV can an HIV test if I am infected?. If you get an HIV test within 3 months after a potential HIV exposure and the result is negative, get tested again in 3 more months to be sure.