Confused about rapid tests? Here’s what to know.


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The federal government in January launched a website so that people in the United States can order free at-home antigen test kits in response to the surge in coronavirus cases and hospitalizations.

But many people remain confused about these rapid tests and how they work. If you’re one of them, don’t worry. We’ll break down just how reliable these tests are and what your next move should be if you’re looking to get tested.

What is an at-home rapid antigen test, and how does it differ from a PCR test?

Most at-home tests are rapid antigen tests that look for specific proteins of the virus to detect infection. These tests usually provide results in 10 to 15 minutes using samples collected with a nasal swab, but tests might differ in how the samples are used, so be sure to pay attention to the instructions. The swab also usually doesn’t go up the nose as far as the infamous deep nasal swab that feels like “being stabbed in the brain.”

At-home antigen tests can be less reliable than PCR tests, a type of molecular test that looks for the virus’s genetic material (RNA). PCR tests are able to detect lower levels of the virus that antigen tests might miss.

That means that results can be different depending on when the test is done, as the viral load changes over time.

Most PCR tests require a laboratory to perform the test and can take several days to return a result. However, at least two authorized at-home molecular tests don’t require a prescription: the Cue coronavirus test and the Lucira test kit.

How much can I trust a rapid antigen test?

Although PCR tests are generally more reliable, at-home antigen testing can still be useful if you know what to look for. Take a look at the following situations that might apply for those getting tested:

I am not showing symptoms

Your test may immediately flag you as positive, but be cautious even if it claims you are negative. As mentioned above, antigen tests aren’t as sensitive as PCR tests, which means you may be in the earlier or later stages of the infection where the amount of virus being produced isn’t large enough to detect but enough to make you infectious.

People with high viral loads — in the center of the graph above — might still be asymptomatic, making it important to continue isolating.

But regardless of whether you have a low or high viral load, if you’ve been exposed and get a negative result, the best thing for you to do next is to keep isolating and testing yourself, because the viral load may change as time goes by.

If you still get a negative result after about five days of isolation, you’re probably not infected. The Centers for Disease Control and Prevention recommends people isolate for five days “if they are asymptomatic or their symptoms are resolving (without fever for 24 hours)” and to “follow that by 5 days of wearing a mask when around others.”

I’m actively showing symptoms

If you’re symptomatic, an antigen test will be more reliable because your body is putting out a lot more virus to detect. A scientific review published by the Cochrane Library found that in people with confirmed covid-19, the tests correctly identified infections in about 72 percent of people with symptoms.

If you’re experiencing symptoms but get a negative test result, consider retesting yourself a few days later. False negatives are still possible even if your viral load is easier to detect.

At-home antigen tests can sometimes result in false positives, but experts say that false negatives are much more likely. To double check, you can contact your physician and consider scheduling a lab-based PCR test.

A positive test, however, does not mean you should rush to the emergency room. “Seeking testing at an emergency room — without an urgent or emerging medical need — diverts critical, lifesaving resources from people who are truly experiencing an emergency,” according to a news release from Johns Hopkins Medicine.

So the best move if you’re asymptomatic or experiencing mild symptoms? Continue isolating and contact your health-care provider and anyone you may have exposed.

Shelly Tan is a graphics reporter and illustrator specializing in data visualization and illustrative storytelling. She designs and develops interactive graphics.