If you’ve been to a pharmacy recently, you may have noticed that there are now over-the-counter COVID-19 antigen tests that can be purchased. They are inexpensive, easy to use and deliver COVID-19 test results within minutes.
Health authorities have said that rapid antigen testing is a useful public health tool that can help us better screen for infections and slow down the spread of coronavirus. The tests are not as sensitive as the PCR tests most places have relied on throughout the pandemic, but infectious disease experts say the rapid tests are excellent for quickly identifying infected individuals who may be highly contagious.
If you have symptoms and suspect you may have COVID, most infectious disease doctors recommend skipping the rapid antigen test and going straight to PCR. There are treatments that can help people at the beginning of their disease, so if you are symptomatic, “you want a test that can effectively diagnose disease with COVID, and the antigen test is probably not that test. It’s best. thought of as a test to be really contagious, ” Sheldon Campbella pathologist, microbiologist and professor of laboratory medicine at the Yale School of Medicine, HuffPost reported.
How do fast antigen tests work?
Quick tests scan for antigens (a protein located on the surface of the virus). PCR diagnostic tests look for the genetic material of the virus or RNA.
The biggest difference between rapid tests and PCR tests is how sensitive they are. PCR tests are incredibly sensitive and can detect very small traces of viruses. Quick tests, on the other hand, are very insensitive – especially in people who have no symptoms.
Although they could miss small amounts of virus, they are good at identifying large amounts. “You have to have a lot of viruses to make the antigen test positive,” Campbell said.
A large meta-analysis from March 2021 showed that rapid antigen tests detected about 72% of the symptomatic cases confirmed positive by a PCR test. The rapid tests were less sensitive to asymptomatic infections and captured on average about 58% of these cases.
“These rapid antigen tests, especially the popular ones, are not good for detecting patients who are asymptomatically infected,” he said. Benjamin PinskyMedical Director of Stanford’s Clinical Virology Lab.
But that does not mean that the fast antigen tests are useless – and they can even get better. A December 2021 study showed that BinaxNOW’s COVID-19 antigen test identified 87% of symptomatic cases and 71% of asymptomatic cases when performed by healthcare professionals in a controlled environment. Of course, that number is likely to drop a bit when you perform them at home due to issues like user errors. Other things surveys have found that rapid antigen testing captures most cases (93%) that have a solid chance of being transmitted. The rapid antigen tests do this by their ability to identify large viral amounts, indicating that a person may be quite contagious. (People with less viral load are generally thought to be less contagious than those with high viral load.)
“A person who is antigen-negative but PCR-positive is almost certainly less contagious than a person who is antigen-positive and PCR-positive,” Campbell said, adding that further research is needed to determine how contagious a person is that produces a negative fast. test, but a positive PCR test.
What kind of quick test should I buy?
Each set often comes with two home tests. When shopping, look for a label approved by the Food and Drug Administration. These include:
Abbotts BinaxNOW, which you can get from places like CVS for $ 23.99, Walgreens for $ 23.99, Walmart for $ 14, Sam’s Club for $ 14, or RiteAid (prices vary). You can also order through the company website for $ 23.99.
Quidel QuickVue, which you can buy from places like Walgreens for $ 23.99, CVS for $ 23.99, Walmart for $ 24.95 and other pharmacies. You can also grab a set from Amazon.
iHealths COVID-19 Antigen Quick Test, which you can buy on Amazon for $ 17.98. You can also purchase sets from the company website for $ 13.98.
On / Go’s COVID Rapid Test Kit, which you can buy at Walgreens for $ 23.99, Amazon for $ 24.88, Walmart for $ 29.99 or even Best Buy for $ 29.99. The company’s website also sells sets for $ 29.99.
Ellume, another brand approved by the FDA, is another option. However, the FDA withdrew more than 2 million Ellume tests in November due to higher incidences of false positives. The tests concerned were those manufactured between 24 February and 11 August and those distributed between 13 April and 26 August.
Many of these kits tend to sell out quickly due to high demand, so it may be worthwhile to have some handy ones in your medicine cabinet (more on storing them in a minute) or sign up to be notified when more set is in stock.
If you are sick or do not want to be with others, many dealers offer pickup next door. Finally, experts recommend avoiding buying from unverified sellers, retailers or through social media. That’s of course because there’s fake test kits out there.
When should I use fast antigen tests?
The question of when and how we should use rapid antigen testing is hotly debated in the medical community. Many health experts say the tests are not sensitive enough to detect all infections. Others claim that quick tests identify the most useful thing: people who can be highly contagious.
Campbell said the best time to use a quick test is just before you are around a large group of people.
“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 just before you do something risky, so you’re not the one, that spreads disease there, ”Campbell said.
If you want to test yourself, the most careful thing to do is to take a PCR test a few days after being exposed or doing something risky. But they are harder to get hold of. If you choose a quick antigen test – especially before you visit someone who is in the high-risk group for severe COVID – wash yourself as close to your visit as possible, Campbell said.
If you have symptoms such as cough or fever, you should take a PCR test, not a quick antigen test, Pinsky advised. At this point, you really want to know if it is COVID as there are treatments like monoclonal antibodies that can reduce the severity and duration of the infection.
Pinsky said we should not use rapid antigen testing to rule out infections. Because these tests are not as sensitive, especially with asymptomatic individuals, “a negative result does not mean very much,” Pinsky said.
According to Pinsky, another best use is for them in assembly environments, such as a dormitory or long-term care facility, where they can identify an ongoing outbreak, where individuals are at various points in the infection cycle – some would be recently exposed, others would be newly infected or symptomatic, and have detectable levels of viruses. How to use other rapid antigen tests, such as those used to detect norovirus, traditionally, Pinsky explained.
How to interpret the test results
Access to rapid PCR tests remains a problem, while rapid tests are available at pharmacies. That said, they can be expensive; people are now calling on the government to intervene and offer them for free to households. Especially since a quick antigen test is in many cases the easiest choice.
If you have some on hand, keep in mind that these tests have a shelf life that ranges from six months to a year. You can keep them until the expiration date printed on the box, but do not use them beyond that.
If you have no symptoms but take a quick antigen test for screening purposes and test negative, it is not a guarantee that you are ready. However, it is an indication that even if you were infected, your viral load probably would be too low to transfer. There is always a chance that you have small amounts of virus that the test just did not detect, or that you may become contagious within a few days. This is why so many fast antigen tests recommend testing again the next day.
If you have symptoms and get a negative quick test result, tread carefully, Pinsky said. Although it is generally believed that people who produce a negative fast antigen test are not as contagious as they have smaller amounts of virus, there is still a chance that they can become infected and excrete small amounts of the virus, which can then be transmitted. It is not yet known exactly if and how contagious a person with a small amount of virus can be.
Finally, if you take a quick antigen test and get a positive result, it is a pretty sure sign that you are infected, but as is the case with any diagnostic test, false positives Spoon.
“If you’re antigen-positive, you have a lot of viruses and are probably quite contagious,” Campbell said.
This story has been updated. Experts are still learning about COVID-19. The information in this story is what was known or available at the time of publication, but the guidelines may change as scientists discover more about the virus. Please check the Centers for Disease Control and Prevention for the most up-to-date recommendations.
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This article originally appeared on HuffPost and has been updated.