What kinds of tests are available for COVID-19?
PCR tests (nasal swab), rapid antigen tests, antibody tests and T cell tests.
Information about testing is available from the FDA in the following languages:
What is a PCR test?
The Polymerase Chain Reaction (PCR) test is given to see if a person has the virus that causes COVID-19, SARS-CoV-2. Samples are taken from places in the body where the virus is most likely to be found, like the back of the nose or mouth. RNA, which is part of the virus particle, is extracted and converted to complementary DNA for testing. (Sometimes you will see this test referred to as the RT-PCR test. RT stands for Reverse Transcription and refers to this process of converting the RNA to DNA for the purpose of conducting this test.)
Generally, a positive test means the person has COVID-19 and can transmit the disease to others, so please exercise caution and isolate yourself from others if you receive a positive result. It is possible to test positive for the virus and have no symptoms. Asymptomatic people can still transmit the virus to others.
Will a PCR test tell me if I had the virus in the past and had no symptoms or if I have already recovered?
No. If you have recovered, the PCR test will not tell you if you had COVID-19 in the past. The only test that can answer this question is an Antibody test or a T cell test. If you test positive for antibodies or T cells, then you have had a recent or past infection. However, some people report having tested positive for COVID-19, but negative for antibodies.
If I no longer have symptoms, can I still test positive for COVID-19?
Yes. Positive tests results have been reported in people who have recovered; however, scientists think that these results are likely due to faulty tests, or the tests picking up dead particles of the virus that remain in your system, rather than a case of re-infection with COVID-19. Some cases of re-infection have been confirmed however, and information is changing rapidly, so continue to check in with your health-care provider if you receive a positive test result.
What is a rapid Antigen test?
The Antigen test is used to detect an active viral infection. The main advantage of antigen tests, according to the FDA, is the speed at which they can provide results (advertised as within 15 minutes), whereas PCR test results can take a few days. Specimens for testing are collected using a nasal swab. Antigen tests are cheaper and easier to use, compared to other viral tests available. The main disadvantage of antigen tests are their high false-negative rates compared to molecular RT-PCR tests.
Antigen tests are now available to be administered at home. They typically can be found at major pharmacies. Additionally, please check out https://www.covidtests.gov if you are a US resident to receive four free COVID at-home antigen tests for your household.
What is an Antibody test?
Antibody tests, or serology tests, look for antibodies in the blood. These antibodies form as a person is recovering from COVID-19 and fighting the disease.
Antibody tests analyze blood, serum or plasma samples for the presence of immunoglobulin M [IgM] and immunoglobulin G [IgG]. IgM and IgG are antibodies associated with the coronavirus (SARS-CoV-2). IgM forms in the body as it first begins to recover and provides the first line of defense during viral infections. IgG forms next and provides longer-term immunity and immunological memory.
If I test positive for antibodies, am I no longer contagious?
Not necessarily. Antibodies form in the body to help you fight disease. The detection of COVID-19 IgM antibodies tends to indicate a recent exposure to COVID-19, and detection of COVID-19 IgG antibodies indicates a later stage of infection - and that the patient has started to recover. The CDC’s present guidance states that people with COVID-19 should be isolated for at least 10 days after symptom onset and until 24 hours after their fever subsides without the use of fever-reducing medications.
If I test positive for antibodies, am I immune to later infection?
Not necessarily. It is not known at this time if, or for how long, IgG antibodies confer immunity to COVID-19, but researchers believe that they most likely convey some level of protection against future infection. That protection may be short lived, and may vary from person to person.
How accurate are Antibody tests?
In general, even the best tests are not 100% accurate. As of February 10, 2022, 85 tests have received Emergency Use Authorization [EUA] from the FDA. EUAs are issued for each individual test with certain conditions of authorization required of the manufacturer and authorized laboratories. However these tests have not been ‘FDA Approved’, as they have not undergone thorough testing for accuracy. False positive and negative results are possible. A review of the tests that have received EUA by the FDA:
www.fda.gov/medical-devices/emergency/eua-authorized-serology-test-performance
As you read the above link, you will need to understand the following terms.
"Sensitivity" is the ability of a test to correctly identify those patients with the disease (true positive rate).
"Specificity" refers to the ability of the test to correctly identify those people without the disease (true negative rate).
The Positive [PPV] and Negative Predictive Values [NPV] are the proportions of positive and negative results that are true positive and true negative results, respectively.
The efficacy of all diagnostic tests for COVID-19 also depends on the dominant COVID strain / strains spreading in the community. As the Sars-CoV-2 virus evolves over time, PCR, antigen, and antibody tests are affected by viral mutations differently due to the inherent design differences of each test. For example, the sensitivity of antigen and specific PCR tests to the omicron variant is believed to be reduced based on early data.
Can you test positive for both the virus and the antibodies?
It is possible to test positive for antibodies, and still test positive for the virus (with a PCR test). This means that your body is producing the antibodies to fight the virus, but at the same time you still are recovering. This is possible, even if you aren’t showing any of the classic COVID-19 symptoms.
What is a T cell test?
Adaptive technologies recently released a T cell test for COVID-19. T cells are part of the body's immune response and are what tell the body to produce antibodies. Some T cells also fight off disease directly. A T cell test, like an antibody test, can tell a person if they previously have been infected by the virus, whether or not they displayed symptoms. Traditional blood tests can detect the presence of antibodies in the blood, indicating that the body has responded to an infection in the past, but antibodies appear to decrease over time. Moreover, recent studies show that some people never mount a detectable antibody response and are instead able to fight off the infection with other immune cells, T cells, before antibodies even appear. Having different tests to help detect recent or past infection is critical to gaining a more accurate understanding of immunity on a population-wide scale. Read more about T cells in our FAQ Immune System section.
What is the difference between all the tests?
PCR and Antigen tests are diagnostic tests that are used to diagnose an active COVID-19 infection. Specimens for testing are collected using a nasal swab and a positive PCR test reflects an active viral infection. According to the FDA, Antigen tests are not as specific at PCR tests, and may result in more false negatives. However, results are available more quickly.
Antibody tests and T cell tests assess a body’s immune response to the virus in order to determine whether a person has previously been exposed to COVID-19. Both tests are done through a blood draw. A positive test reflects recent or past infection.
Can the tests be wrong?
Yes. Diagnostic tests for COVID-19 have a 20-30% false negative rate (antigen tests have higher false negative rates than PCR tests). These rates are higher if you test earlier than 4 days after exposure. That means if you get a negative result on your test, you could still be positive. If you feel sick and get a negative test result, you should still take precautions so that you do not spread your illness to others. False positive test results are less likely. If you have been exposed, the safest course of action is to self-isolate for 14 days.
The efficacy of diagnostic tests for COVID-19 also depends on the dominant COVID strain / strains spreading in the community. As the Sars-CoV-2 virus evolves over time, PCR, antigen, and antibody tests are affected by viral mutations differently due to the inherent design differences of each test. For example, the sensitivity of antigen and specific PCR tests to the omicron variant is believed to be reduced based on early data.
After exposure to someone with COVID-19, how soon should I get tested?
If you test too early, you are likely to get a false negative result. If you have been exposed to someone who tested positive, you should self-isolate for 4-5 days after exposure and then get tested. Results will likely be most accurate 5 days after exposure. You should continue to self-isolate after testing until you receive your results.
Where can I get tested?
Many states are offering free PCR tests at multiple drive thru locations including hospitals, medical clinics, churches, and stores such as CVS. A Google search for "covid test" and your state or city should bring up sufficient results. You can also visit the US Department of Health and Human Services website to find their ‘Community-Based Testing Sites for COVID-19’ test locator or take a look at this spreadsheet, which provides a list of COVID and Antibody testing locations in each US state.
Antibody tests are also available. Many testing locations require a referral from a health care provider. Please check with your healthcare provider. Multiple national health testing companies are offering antibody tests such as:
● Quest: https://www.questdiagnostics.com/home/Covid-19/Patients/
● PM Pediatrics: https://pmpediatrics.com/covid-antibodytesting/
● Arcpoint: https://www.arcpointlabs.com/covid-19-antibody-testing/
● Labcorp: https://www.labcorp.com/coronavirus-disease-covid-19/patient-information/covid-19-testing-options
