Which Test Should You Use After Exposure to COVID?

If you’ve been in close contact with someone who tested positive for COVID-19, you're going to need to get tested.

Your vaccination status determines whether you need to get tested right away or need to wait a few days after exposure. But what test should you use? With the increased availability of rapid at-home COVID-19 tests, it can be difficult to figure out which test is right for your current needs.

You have two options: rapid (or antigen) tests or reverse transcriptase-polymerase chain reaction (RT-PCR) tests. The first is what you can typically scoop up at the pharmacy, a rapid test that can give you results at home in minutes. PCR is your standard COVID-19 test that needs to be sent to a lab.

Although antigen and PCR tests are both used to detect an active COVID-19 infection, their sensitivity to the virus is not the same. Here’s what you need to know about the difference between the two.

What’s the Difference Between Antigen and PCR tests?

“Rapid antigen tests are designed to detect the presence of a viral protein or antigen, while RT-PCR tests are designed to detect the presence of viral genetic material, or viral RNA,” Ashley Lipps, MD, infectious diseases physician at The Ohio State University Wexner Medical Center, tells Verywell. “Both types of tests are generally accurate, although RT-PCR tests are more sensitive than antigen tests, meaning, less likely to get a false negative result. The benefits of antigen testing are that the results are available quicker and are less expensive.”

Rapid antigen tests require a higher level of the virus to be present before turning positive. On the other hand, PCR tests can remain positive as long as it detects any small virus material, even when you're not contagious anymore.

“RT-PCR tests detect the viral genome after amplifying a small target section millions of times,” Sheldon Campbell, MD, PhD, FCAP, associate director of Yale Medicine’s clinical microbiology lab and professor of laboratory medicine at Yale School of Medicine, tells Verywell. “Because of the amplification step, RT-PCR tests are more sensitive than rapid antigen tests.”

Although the PCR test is more sensitive, neither test is perfect and there’s always a small chance you might get a false result. Sometimes getting a second test is recommended.

Which Should You Use?

According to the CDC, fully vaccinated individuals do not need to quarantine after a potential COVID-19 exposure if they are asymptomatic, but they should still get tested five to seven days after exposure.

“Unless you have symptoms, an antigen test is likely adequate for this purpose,” Campbell says. “If you have symptoms, use a PCR test. It’s more sensitive, and diagnosing COVID infection is critical both for prevention and treatment with medications that can prevent more severe disease.”

If you are not fully vaccinated, you need to quarantine for 14 days after potential COVID-19 exposure and watch out for any symptoms. However, the quarantine period generally varies depending on the circumstances outlined by your local public health department.

“For individuals who are not fully vaccinated, testing should be done at the time the exposure is known and again in another five to seven days if the initial test is negative,” Lipps says. “Either a rapid antigen or RT-PCR test can be used, but RT-PCR tests do have higher sensitivity.”

Is It Necessary to Get Tested Twice?

Unvaccinated people should get tested immediately after exposure. If the test comes back negative, they should take a second test five to seven days after the initial one or if symptoms develop.

“Under most circumstances, using one type of test will suffice,” Lipps says. “However, there may be certain circumstances where your healthcare provider may recommend a second test.”

If you think there's a good chance you have COVID-19 but your rapid test is negative, you can get a PCR test since antigen tests have higher rates of false negatives, she adds. For instance, the CDC recommends that people who are symptomatic but received a negative antigen test result need to confirm those results with a PCR test to avoid delays in diagnosis, treatment, and infection control.

While testing after a potential exposure is necessary, experts also emphasize the importance of testing before attending any gathering where you might transmit the virus if you carry it without your knowledge.

“The most important time to get a COVID test is before you do something risky, like going to a crowded event or meeting with a vulnerable loved one, not after the fact,” Campbell says. “The antigen test seems to be a reasonably good test for being infectious. It’s best used to manage risk, to test before being in a setting where you might spread COVID to others.”

The information in this article is current as of the date listed, which means newer information may be available when you read this. For the most recent updates on COVID-19, visit our coronavirus news page.