If you took advantage and signed up for a free government-sponsored at-home Covid Test, it should have arrived by now (or will be soon). The Biden administration said it would send 500 million rapid tests to Americans this month via the U.S. Postal Service after the Omicron variant strained access to in-person and at-home tests. (If you haven’t yet, you should know that each household is eligible for four free rapid tests and can order them at covidtests.gov.)
If you’ve never used an at-home test, here are the FAQ’s.
Are Rapid Antigen Tests as accurate as the PCR for detecting Covid?
Health officials have said rapid antigen tests are a useful public health tool that can help us better screen for infections and slow the spread of the coronavirus. The tests aren’t as sensitive as the PCR tests most places have relied on throughout the pandemic, but infectious disease experts say the rapid tests are excellent at quickly identifying infected individuals who may be very contagious.
A large meta-analysis from March 2021 found that rapid antigen tests detected about 72% of symptomatic cases confirmed positive by a PCR test. The rapid tests were less sensitive with asymptomatic infections, catching on average about 58% of those cases. “These rapid antigen tests, particularly the popular ones, are not good at detecting patients who are asymptomatically infected,” said Benjamin Pinsky, medical director of Stanford’s Clinical Virology Lab.
But this doesn’t mean the rapid antigen tests are useless ― and they might even be getting better. A December 2021 study found that BinaxNOW’s COVID-19 antigen test identified 87% of symptomatic cases and 71% of asymptomatic cases when performed by health care workers in a controlled setting. Of course, that number is likely to go down a bit when conducting them at home because of issues like user error. Other studies have found that rapid antigen tests catch most of the cases (93%) that have a solid chance of being transmissible. The rapid antigen tests do this by their ability to identify large viral loads, which indicate a person could be pretty contagious. (People with smaller viral loads are generally believed to be less contagious than those with high viral loads.)
When is the best time to use a Rapid Antigen Test?
The question of when and how we should be using rapid antigen tests is heavily debated in the medical community. Many health experts say the tests aren’t sensitive enough to pick up on all infections. Others argue that rapid tests identify the most useful thing: people who may be highly infectious.
Experts say that the best time to use a rapid test is right before you’re around a large group of people. “By far the most important time to use an antigen test is not three to five days after you did something risky to find out if you’ve already suffered the consequences — it’s right before you do something risky so you aren’t the one who spreads disease there,” says Sheldon Campbell, a pathologist, microbiologist, and professor of laboratory medicine at Yale School of Medicine.
If you want to test yourself, the most prudent thing to do is take a PCR test a few days after being exposed or doing something risky. But they’re harder to come by. If you’re opting for a rapid antigen test ― particularly before you’re visiting someone who is high-risk for severe COVID ― swab yourself as close to your visit as possible, Campbell said.
If you have symptoms, like a cough or fever, you should take a PCR test, not a rapid antigen test, Pinsky advised. At this point, you really want to know if it’s COVID, since there are treatments like monoclonal antibodies that may reduce the severity and duration of the infection.
Do the Rapid Antigen Tests Expire?
How do you interpret the Test Results?
If you don’t have symptoms but take a rapid antigen test for screening purposes and test negative, it’s not a guarantee you’re in the clear. It is, however, an indication that even if you were infected, your viral load probably would be too low to be transmissible. There is always the chance that you have small amounts of virus that the test just didn’t pick up, or that you could become contagious in a couple of days. This is why so many rapid antigen tests recommend retesting the next day.
If you have symptoms and get a negative rapid test result, still be cautious, Pinsky said. Though it’s generally believed that people who produce a negative rapid antigen test aren’t as contagious, since they have smaller viral loads, there’s still a chance they could be infected and shedding small amounts of the virus, which can then be passed on. It’s not yet known exactly if and how contagious a person with a small viral load may be.
Finally, if you take a rapid antigen test and get a positive result, that’s a pretty sure sign you’re infected, though as is the case with any diagnostic test, false positives do happen (although they’re rare). “If you’re antigen-positive, you’ve got quite a bit of virus and are probably pretty contagious,” Campbell said.
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