Instances of false negatives and false positives after a COVID-19 test are rare, but it is important to better understand each and what they might mean for you. In order to protect yourself and the people around you, you should still wear a mask and practice social distancing at all times.
Though uncommon, it could be possible to get a false negative COVID-19 test. This means your test results indicate you are negative for the COVID-19 virus, but the virus is actually in your system. The most likely reason for a false negative is if you were very recently exposed to the virus and have a very low viral load in your system. The incubation period for COVID-19 is anywhere from 3-14 days, so if you were exposed to someone with COVID-19, it is actually beneficial for you to wait at least 3 days before getting tested in order to avoid a false-negative result.
The PCR test for COVID-19 is the most accurate at determining if you have the virus because it looks for genetic material specific to COVID-19 in your test sample. Because this test is considered the gold standard, it is less likely that you would encounter a false negative. If your viral load is low enough in the first few days after exposure, it is possible that not enough genetic material is present to register on the test. In general, rapid COVID-19 tests are not as sensitive as the PCR test so a false positive is possible, though also not common.
False positives are even less likely with COVID-19 tests, though it is possible that a COVID-19 test could actually detect other coronaviruses in your system. This would be most likely with an antibody test, which looks for evidence of you already having had the virus. An antibody test may deliver a false positive if you have recently been ill with another type of coronavirus with similar antibodies. It is possible, though unlikely, that you could receive a false-positive result if your sample is contaminated during processing.
While the risk of a false negative or false positive is low, it is important to practice social distancing and wear a mask when around other people to help mitigate the spread of COVID-19. A false-negative test result could cause someone to think they are free to interact with others in close proximity, providing a false sense of security to those around you. A false positive may cause you stress, especially if you have not developed any symptoms. However, with both false negatives and positives, if you are following guidelines for staying safe and taking precautions then you are less likely to risk unnecessary exposure to yourself or others.
Because false negatives and false positives are uncommon, you should follow guidelines and recommendations from healthcare providers for what to do after you test positive or negative. If you test positive, there are steps to take to protect yourself and others, like isolating or self-quarantining. If you test negative, this does mean you are still at risk for getting COVID-19 and should take every precaution to avoid infection.