(NEXSTAR) — The federal government is preparing to send Americans free at-home COVID-19 tests as cases of the virus remain high nationally. But once you take a test at home, when should you really test again?

The answer depends mostly on which test you have, according to the Centers for Disease Control and Prevention. Some tests are intended to be used in a series, meaning they will instruct you to test multiple times for the most accurate result. Others may provide instructions on performing serial testing.

Serial self-testing is when you test yourself multiple times or on a routine basis. Frequent testing can help detect SARS-CoV-2 more quickly, according to the CDC, and can help reduce the spread of the virus.

If you self-test and receive a negative result, the CDC recommends following the manufacturer’s instructions for use for serial testing. Some kits may recommend testing again within two or three days.

The BinaxNOW COVID-19 Antigen Self Test, for example, instructs those who first test negative to test again within three days with at least 36 hours between tests. If your first or second test is positive, you likely have COVID-19 in your system and should enter isolation.

Another, the QuickVue At-Home OTC COVID-19 Test with two testing kits, is intended for use over different testing timelines. People that are experiencing symptoms are expected to test more frequently than those who aren’t.

According to the instructions for the CareStart COVID-19 Antigen Home Test, those who do not have COVID-19 symptoms should do at least two tests. This kit describes serial testing as testing each day or every other day.

If you do test positive with any of your tests, CDC guidelines say you should enter isolation. Isolation isn’t different from quarantine — it’s mainly semantics. You will still have to stay home for a few days, depending on your vaccination status. Currently, the CDC is not “expressly recommending” that you need to test negative before leaving isolation.

“Instead [use] a time-based strategy that considers symptoms to determine the best time to end isolation,” an agency spokesperson told Nexstar last week. So you can test as many times as you like while in isolation, but current guidance says you should rely on your symptoms rather than a negative test to end your time indoors.