How Accurate Are Homemade Kovid Tests?


In the early months of the pandemic, getting a coronavirus test often required visiting a health center, laboratory, or special testing site, a process that sometimes involved long queues and waits. a week or more to get results.

americans can now take rapid virus tests from the comfort of their own home. Most of these tests are available without a prescription and give results in just 15 minutes.

Demand for testing has increased in recent months as the highly contagious Delta variant spread and schools and offices reopened. “All manufacturers are ramping up production, but it can be difficult to find them right now,” said Gigi Gronvall, a tester at Johns Hopkins University.

Experts said that while rapid tests have their limitations, they are an important public health tool, especially if you know how to use them.

“Having this information and being able to make better decisions is very powerful,” said Mara Aspinall, a biomedical diagnostician at Arizona State University, who is on the board of OraSure, which makes rapid Covid tests. “And the ability to do that on a wait a while basis was something we couldn’t do a year ago.”

A handful of rapid home tests are available without a prescription, including the Abbott BinaxNOW, Ellume Covid-19 Home Test, and the Quidel QuickVue Home Covid-19 Test. Prices range from about $10 to $40 per test, but President Biden has announced plans to cut prices by roughly a third.

All three detect small viral proteins called antigens. The tests require running a shallow nasal swab into your nostrils and then exposing the swab to a few drops of the chemical. They give results in about 15 minutes.

The tests themselves are pretty straightforward, but each involves a slightly different procedure that must be followed literally. “If you’re doing home tests, you should read the instructions and follow them meticulously,” said Patrick Godbey. Former president of the American College of Pathologists.

Dr. Aspinall agrees. “This is not the time for creativity,” he said.

Typically considered the gold standard for detecting the virus, polymerase chain reaction tests are typically performed in a laboratory and involve making many copies of the virus’s genetic material. This process helps PCR tests detect even minute traces of the virus..

Rapid antigen tests that do not amplify the virus are less sensitive than PCR tests. The test may give a false negative if you get one at the earliest stage of an infection, before the virus has replicated widely.

Some of the home antigen tests They have an overall sensitivity of roughly 85 percent, which means they catch roughly 85 percent of people who are infected and 15 percent miss it. In some studies, real-world performances got even lower.

But tests work better Studies have found that in people who have no symptoms and are most susceptible during the first week of symptoms.

Experts said that antigen tests are excellent at marking people with a high viral load and therefore more likely to actively transmit the virus to others.

Dr. “The more virus you have in your nose, the more virus you get into the air, and the more virus other people can inhale,” Gronvall said. “The tests are very accurate and correlate very well with PCR, where humans are most contagious.”

Using tests repeatedly—for example, to routinely screen students for the virus— can compensate lower sensitivities. Inside a new studyWhen the researchers tested infected college students and staff every three days, they found that rapid antigen tests successfully detected 98 percent of infections on par with PCR tests.

At-home rapid tests are a good option for people who have been exposed to the virus, want to know if their sore throat is from Covid-19 or just the common cold, or want a little extra reassurance before visiting a vulnerable relative. or after traveling to a virus hotspot, experts said.

Experts said people with symptoms can get a rapid antigen test right away, but people known to have been exposed to the virus should wait three to five days before doing so. Testing too early before the virus has had a chance to multiply increases the chance of a false negative.

“And that’s a critical, critical piece,” said Ms. Aspinall. “There are a lot of people who get on the plane, get off the plane and say, ‘I’m negative – I can visit my grandma.’”

However, some businesses, travel authorities and other organizations may not accept the results of home tests when proof of a negative test result is required.

Rapid antigen tests work best when used in series. If you test negative after possible or known exposure to the virus, Experts said you should have a second test a day or two after you develop Covid-19 symptoms.

Dr. “Testing is a moment in time,” Gronvall said. You don’t know the day or the hour when the virus “breaks through your immune defenses”.

But he noted that until tests become cheaper and more readily available, it may be difficult to persuade people to use them frequently. Dr. “We definitely need more testing in the market and they’re more cost-effective,” Gronvall said.

Rapid antigen tests are highly specific, which means they produce few false positives. Dr. “If your test is positive, the error rate is pretty low,” Gronvall said.

If you test positive, you should self-isolate, monitor your symptoms, and seek medical attention if needed.

Consumers should also report positive results to their local health authorities.

“If we don’t report the tests properly, we still won’t have a good idea of ​​the true caseload – how many people running around might be contagious, which could be passing it on to other people,” Godbey said. .



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