Testing for SARS-CoV-2 Infection
Test Types
Viral tests, including nucleic acid amplification tests (NAATs, such as PCR tests), antigen tests and other tests (such as breath tests) are used as diagnostic tests to detect current infection with SARS-CoV-2, determine the need for prevention measures like isolation, and inform an individual’s medical care. Viral tests can also be used as screening tests.
Viral tests:
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- Nucleic acid amplification tests (NAATs) are highly sensitive and highly specific tests that detect one or more viral ribonucleic acid (RNA) genes. PCR tests are the most common type of NAAT used for COVID-19 testing. Viral RNA may stay in a person’s body for up to 90 days after they test positive. Therefore, NAATs should not be used to test someone who has tested positive in the last 90 days. Most NAATs need to be performed in a laboratory, although some are performed at the point-of-care. Most NAATs produce qualitative (positive/negative) results.
- Antigen tests are immunoassays that detect the presence of specific viral proteins, called antigens. A positive test indicates current infection. Antigen tests generally have high specificity, similar to NAATs, but are less sensitive than most NAATs. Because antigen tests have lower sensitivity, FDA recommends that negative antigen tests be repeated up to three times, with each test 48 hours apart to confirm a negative result. Most antigen tests are less expensive than NAATs and can provide results in minutes. Antigen tests are available for at-home testing (self-testing), at the point of care, or in a laboratory.
- As noted in the labeling for authorized over-the-counter antigen tests: Negative results should be treated as presumptive (meaning that they are preliminary results). Negative results do not rule out SARS-CoV-2 infection and should not be used as the sole basis for treatment or patient management decisions, including infection control decisions. Please see FDA guidance on the use of at-home COVID-19 antigen tests.
- Other diagnostic tests may be used to detect SARS-CoV-2 from non-traditional respiratory specimens, such as breath. These tests’ results may be presumptive and require confirmation by NAAT. Please refer to each test’s Instructions for Use (IFU) for specific interpretation.
Positive viral test results indicate current, or sometimes recent, infection and the person with COVID-19 should follow CDC recommendations for isolation.
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Negative viral test results mean the test did not detect the virus, but this doesn’t rule out that you could have an infection. These results represent a snapshot of the time around specimen collection and could change if the same test was performed again in one or more days. Negative antigen test results should be repeated following FDA guidance.
Antibody (or serology) tests are used to test for the presence of antibodies from previous infection or vaccination and can aid in fulfilling the case definition for multisystem inflammatory syndrome in children (MIS-C) and adults (MIS-A).2 Antibody testing does not diagnose current infection. Antibody testing is primarily used for public health surveillance and epidemiologic purposes. Antibody tests detect specific antibodies that target different parts (nucleocapsid or spike protein) of the virus. Detection of anti-nucleocapsid antibody indicates SARS-CoV-2 infection, while anti-spike protein antibody may be induced by COVID-19 vaccination or by SARS-CoV-2 infection. This should be considered when choosing whether to test for antibodies originating from past infection versus those from vaccination.
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