There are different types of tests for COVID-19 currently available. All have their own limitations, and no test is 100% accurate all the time. If you and your healthcare provider think you have COVID-19, you should take appropriate precautions to avoid spreading it to others even if the test suggests you do not have it. More information about testing is available from the CDC.
- Positive test = test suggests you have the illness
- Negative test = test suggests you do not have the illness, but other factors must be considered such as the timing that the test is done
- Indeterminate test = result was not conclusive, and test should be repeated
Types of tests
1. Polymerase Chain Reaction (PCR) or Nucleic acid amplification test (NAAT): This type of testing, also called molecular or viral testing, is done by swabbing the nose or mouth or collecting saliva. The test detects a part of the virus’s genetic material. It is currently considered the best test to determine if someone was recently infected with the virus, but people can continue to test positive with this test long after they are no longer contagious and are no longer at risk of spreading the virus. CDC provides further information on this type of testing.
- The virus must be present at a level high enough for the test to detect it. There is a delay between the time a person is exposed and the time the virus level gets high enough for the test to be positive.
- A negative test does not rule out the possibility of that person soon becoming sick with the virus. If someone is tested too soon after being exposed to the virus, they may have a negative test even though they will soon become contagious with the virus.
- Someone who has been instructed to quarantine after an exposure to a person with COVID-19 cannot shorten the length of their quarantine period even if they test negative because it is possible they were tested at a time when the virus was not detectable.
- If someone has symptoms of COVID-19, the virus can usually be reliably detected by this test; and a negative test suggests the symptoms are not due to the COVID-19 virus.
- A positive test does NOT necessarily mean that the person is still contagious with the virus. The timing of the symptoms or the test should be used to determine if someone can still spread the virus.
2. Blood test, antibody or serology testing: This testing is done using a sample of blood and detects antibodies produced as a result of the body trying to fight off the virus. These tests are most useful for determining if someone has been exposed to the virus in the past. These tests are NOT recommended to determine if someone is currently infected. CDC provides further information on these types of tests.
- It can take 1 to 3 weeks after the exposure to virus for antibodies to rise to a level high enough for the test to detect them. You may be currently infected but have a negative antibody test.
- We are still learning about these tests and whether or not the antibodies they detect could protect against future infection. No one should consider themselves immune to COVID-19 infection based on these results. Precautions should still be taken to protect against future infections, even if you test positive for antibodies.
3. Antigen tests: These tests are done by swabbing the nose. Instead of detecting the virus’ genetic material, they detect a protein on the virus. These are often available as “rapid” tests that can be done in medical offices. The faster results make this a very useful test.
- These tests may not detect lower levels of virus and could produce more “false negatives.” Results of these tests should be interpreted with that in mind.
Those who test positive on a viral test (PCR or antigen) do not need additional testing within the three (3) months following symptom onset or test specimen collection.