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What type of COVID-19 test should I get and when should I get it? What’s the difference between a molecular/PCR, antigen, and antibody test?

Last Updated: 09/26/2022

If you want to find out if you are currently infected with COVID-19, get a diagnostic test.

Testing is widely available and open to everyone in New Jersey. Visit covid19.nj.gov/testing to find a testing location near you.

It's especially important to get tested if:

  • You have COVID-19 symptoms, regardless of your vaccination status or if you recently recovered from COVID-19 in the last 90 days. Test immediately.
  • You have been in close contact with someone who tested positive for COVID-19. Wait at least 5 full days after your exposure and test on day 6.
  • You are in high-risk settings where screening testing is implemented.
  • You plan to be in contact with someone at high risk for severe illness from COVID-19, especially if you are in an area with a CDC COVID-19 Community Level in Medium or High.
  • You have plans for travel. It is recommended to get tested with a viral test no more than 3 days before travel.

Which test should I get?

If you have not had COVID-19 or have not had a positive test within the past 90 days, a NAAT or antigen test can be used. If an antigen test is used and the result is negative, multiple tests may be needed.

If you tested positive for COVID-19 in the last 30 days and you do not have symptoms, testing is not recommended to detect a new infection.

If you tested positive for COVID-19 in the last 30 days and you have symptoms, use an antigen test. If negative, multiple tests may be necessary.

If you tested positive for COVID-19 in the last 31-90 days, use an antigen test. Multiple tests may be necessary if the result is negative.

After a positive test result, one may continue to test positive for a while after. One may continue to test positive on antigen tests for weeks after an initial positive. One may continue to test positive on a NAAT test for up to 90 days. It is always best to talk with your health care provider about which test is best for you. Please refer to CDC COVID-19 Testing guidance for additional information.

Visit COVID19.nj.gov/testing to get a COVID-19 diagnostic test.

What's the difference between the various test types?

Viral tests, which are diagnostic tests used to look for current infection, detect the presence of SARS-CoV-2, the virus that causes COVID-19, in specimens. There are two main types of viral tests: nucleic acid amplification (NAAT) tests and antigen tests.

NAAT Tests

NAAT tests, such as PCRs, detect viral genetic material which may stay in one's body for up to 90 days after testing positive. They are typically performed in a laboratory and are considered the most reliable tests. A NAAT/PCR test should not be used if an individual tested positive within the last 90 days. Since NAAT/PCR tests are generally performed in specialized labs, it is a relatively slow process. Results on tests done as an outpatient are rarely ready in less than a day and may take much longer.

Antigen Tests

Antigen tests detect specific viral antigen in a specimen and they provide results relatively quickly, usually within 15-30 minutes. Antigen tests are less sensitive than NAAT tests and a single, negative antigen test result should not be used to rule out infection. A negative antigen test should be repeated at least 48 hours apart to best detect infection. A follow-up NAAT/PCR test may be needed to confirm results from an antigen test.

Self-Tests or Home-based Tests

A variety of home-based COVID-19 tests are widely available. While all involve self-collection of specimens, some test kits require a prescription and others are over-the-counter (OTC). Some collections/testing are observed by a telehealth provider, some involve self-collection but are sent to a laboratory for processing, and others use self-collection and self-testing without any involvement of a healthcare provider. Some home-based tests have been authorized by FDA for screening purposes, others for diagnostic testing. At-home antigen tests have not been authorized by the FDA for use in children under 2 years of age. Information on home-based testing is available at https://www.state.nj.us/health/cd/documents/topics/NCOV/COVID_home_tests.pdf.

Self-tests, like all antigen tests, are less sensitive than PCR tests and self-tests are additionally subject to potential sample collection and testing errors. Currently, all at-home COVID-19 antigen tests are FDA-authorized for repeat, or serial use. This means people should use multiple tests over a certain time period, such as 2-3 days, especially when the people using the tests don't have COVID-19 symptoms.

Antibody Tests

An antibody test looks for the body's response to SARS-CoV-2, the virus that causes COVID-19. It is a blood test that is good at determining if youhadthe disease, but not good for determining if youhavethe disease. As such, antibody tests should not be used to diagnose the virus.

While there is evidence that antibodies may provide protection from infection, that has not yet been proven and therefore results of an antibody test should not be used to determine immunity.

Reference: https://www.cdc.gov/coronavirus/2019-ncov/symptoms-testing/testing.html