Studies show antigen tests miss many asymptomatic infections. They work best when you’re having COVID-19 symptoms, Wroblewski said. Common signs of COVID include cough, fever, fatigue, muscle aches, congestion, runny nose, loss of taste or smell, nausea, vomiting and diarrhea, according to the U.S. Centers for Disease Control and Prevention (CDC).
The Cue and Lucira tests use a newer molecular technology called isothermal amplification that is similar to PCR. Like PCR, it works by copying the virus’s genetic material until there are detectable levels.
David Pride, M.D., director of the clinical molecular microbiology laboratory at the University of California, San Diego, says that while molecular tests are generally more accurate than antigen tests because they can detect the virus at lower levels, they are still less sensitive and less specific than a PCR test done in a lab.
For any at-home test, if you have symptoms and you test positive, “it’s very, very likely you have the virus,” Pride said, and you should go into isolation and get in touch with your health care provider.
How confident can you be of a negative result?
A negative test can give you more confidence about going into work or visiting a family member, but experts emphasized that it’s not a free pass to stop wearing a mask, practicing social distancing or taking other precautions.
“The danger is that you’ll have people use these tests to say I can safely go see grandma, when they may be brewing an infection that is below the limit of detection,” said Gary Procop, M.D., medical director in clinical virology at the Cleveland Clinic. “People really need to understand these subtleties, and they’re not all on the package insert,” he added.
Antigen tests, in particular, are likely to miss the virus if you’re early in the infection or if you don’t have symptoms.
A study published by the CDC on Jan. 22 found that Abbott’s antigen test identified only 34 percent of COVID-19 infections in people without symptoms.
A large-scale review of 68 studies published March 24 found that rapid antigen tests identify about 72 percent of people with symptoms and only 58 percent of those without symptoms. Antigen tests are most accurate when used within the first week after symptoms develop, the review found.
The FDA-authorized instructions for use for antigen tests stress that “negative results do not rule out COVID-19 and should not be used as the sole basis for treatment or patient management decisions, including infection control decisions.”
If you test negative but have symptoms, reach out to your health care provider, because there’s a high risk it’s a false negative, Procop said. Your doctor may order a PCR test to confirm your result.
How difficult is it to give yourself a test?
The authorized at-home tests all require you to collect a sample by swabbing your nostrils, either just inside or a little deeper, depending on the test. The good news: You don’t have to insert a swab into the deepest part of your nose like some of the tests performed by health care providers.
As a general rule of thumb, “make sure you’re really swirling it around and hitting skin,” Wroblewski advised. Also, avoid blowing your nose right before you take the test.
All of the tests include detailed instructions with pictures.
When is it better to get the test from a health care provider?
If your symptoms are severe or if you are in a group at high risk of complications from COVID-19, some experts recommend getting tested by a health care provider rather than doing an at-home test.
“With COVID, your oxygen saturation counts can decrease pretty quickly, particularly if you are in a high-risk group, so you want to make sure someone is monitoring your condition,” Wroblewski said.