You’ve probably been hearing a lot about rapid COVID-19 testing lately. Some schools and workplaces are using rapid tests to monitor local transmission rates. Celebs like the Kardashians have even made headlines for hiring concierge testing services to check guests before events like Kendall Jenner’s birthday party.And rapid COVID-19 testing is only going to become more widespread. This week, the U.S. Food and Drug Administration (FDA) even approved the first rapid COVID-19 test for at-home use.

But let’s back up a second: A rapid test manufactured by Abbott Laboratories was given emergency use authorization by the FDA in August 2020. Now, 50 million of these tests are being produced and distributed nationwide every month.

Here’s how the Abbott test works: a nasal swab sample of mucus is twirled onto a sample card treated with a testing reagent. The card reacts to the sample, and if COVID antigens are detected, two lines will appear within 15 minutes.

But how accurate are these tests, and does a negative result mean that you’re COVID-free? “If a person has symptoms, [the tests] are reasonably accurate at diagnosing cases. It’s different when looking at it is a screening test,” says Amesh Adalja, MD, senior scholar at the Johns Hopkins Center for Health Security. That’s because if a person is asymptomatic, they might not have high enough levels of virus in their mucus to test positive.

Experts warn that you shouldn’t treat rapid testing as a free pass to attend a party, wedding, or holiday gathering. “If people think they can test and have a ‘normal’ holiday, we are going to have big increases in cases and hospitalizations and deaths as a result,” says Susan Butler-Wu, PhD, associate professor of clinical pathology at the Keck School of Medicine at the University of Southern California.

With rates of coronavirus on the rise in the United States, here’s everything you need to know about the rapid test.

What is a rapid COVID-19 test?

Generally, there are two common types of tests used to diagnose an active COVID-19 infection: Polymerase Chain Reaction (PCR) tests, which look for traces of the SARS-CoV-2 virus’s genetic material in a patient’s mucus, and antigen tests, which detect the presence of a specific protein on the surface of the SARS-CoV-2 virus. (This protein is called an antigen.) Right now, most PCR tests and all antigen tests rely on nasal swabs, and you should ask your health care provider which test you’re receiving if you’re curious.

At the beginning of the pandemic, the only test available was a PCR test, which with an accuracy rate of 63 to 98 percent is still considered the “gold standard” of COVID testing. In a PCR test, a sample of mucus from your nose or throat is taken using a swab, and shipped to a lab for processing using chemical reagents. In some states, COVID diagnosis can take more than a week using lab-based PCR tests. Some sites may take a saliva sample instead of a mucus sample, per the FDA.

As a result of chemical reagent shortages and processing delays, rapid tests were developed back in the spring. Rapid tests can take as little as 15 minutes, and the majority are antigen tests. (Although the White House and some other locations have a PCR version—the Abbott IDNow—which expedites PCR analysis inside a machine.)

The third type of COVID test, an antibody test, looks for signs that a patient has already had the infection. It’s a finger prick or blood test. Antibody tests are not used to diagnose an active infection. And if you find out that you have antibodies, that doesn’t mean you get a free pass to stop wearing masks or social distance. “You should not assume that because you have antibodies that means you’re immune and you don’t have to worry about catching it or spreading it again,” says Butler-Wu.

Can I do a rapid COVID test at home?

The just-approved Lucira COVID-19 All-In-One Test Kit will be widely available by prescription in early spring 2021, according to manufacturers. The single-use test will cost around $50 and takes about 30 minutes from start to finish. It has an accuracy rate of between 94.1% to 98%, according to Lucira.

Here’s how it works: You swab your nose, and then swirl the sample into a vial of solution. Then, you plug the vial into a small battery-operated device. The machine analyzes the sample with a method called a loop-mediated isothermal amplification reaction (LAMP). Similar to PCR tests, LAMP duplicates the virus’s genetic material until it reaches detectable levels. When the analysis is complete, a light will tell you whether you’re positive or negative.

What are the benefits of a rapid COVID test?

“Number one, they’re rapid. Number two is they don’t require a sophisticated laboratory to process,” says Dr. Adalja. “Number three is they don’t require some of those chemical reagents that are scarce right now. Number four is they’re cheaper.”

Rapid testing also decentralizes testing and makes it more widely available in areas where traditional PCR tests are scarce.

What are the downsides of a rapid test?

Rapid antigen tests may be more likely to result in a false negative or false positive, experts say. Antigen tests, which now comprise most of the rapid testing options on the market, are less sensitive because they look for antigen proteins on the surface of the virus instead of traces of the virus’s RNA. “Antigens tests are never going to be comparable to PCR tests in terms of sensitivity,” Dr. Adalja says. “If you do an antigen test, you may get a false positive like Governor DeWine in Ohio did, or you may get a false negative.”

The Abbott rapid antigen test authorized in August reports a 97.1 percent sensitivity rate, which is very promising. Previously, antigen tests were thought to be 50 to 90 percent accurate, meaning one in two people could get a false result. That said, emergency-use authorization means that “the usual rigorous testing and vetting has not happened, and accuracy results have not been widely published,” Harvard Health Publishing cautions of all COVID tests.

If someone says their rapid COVID test came back negative, does that mean they’re infection-free?

“Testing is something you can do to decrease your risk, but it’s not ironclad,” Dr. Adalja says.

Testing is one of three ways (along with masks and social distancing) to reduce the spread of COVID. Testing, masks, and social distancing are most effective when used together.

“The fact that testing decreases risk is a good thing, but you have to remember it can’t be used alone and you shouldn’t get a false sense of security from it,” Dr. Adalja says.

It’s also important to remember that a COVID test is a snapshot of one moment in time. “It decreases the uncertainty but it’s not going to eliminate it because you know that there’s an incubation period,” Dr. Adalja says.

He cautions that since the test is only looking at a sample during one moment in time, it’s entirely possible for someone to be exposed to the SARS-CoV-2 virus after the test, or be tested during the virus’s incubation period before it would produce a positive result.

If I get a COVID test, can I attend an event like a wedding or a holiday party?

Both Dr. Adalja and Butler-Wu caution that the holidays will need to look different this year to keep COVID transmission under control. “The bottom line is the holidays are going to have to get rethought,” Butler-Wu says. “It is not safe to all be in a room together with the windows closed, even with masks on.”

Since testing isn’t an effective way to contain the spread of COVID without masks and social distancing, it would be wise to change holiday plans accordingly, like going on a hike with extended family, or sitting around a fire or outdoor heater after dinner. “You still want to try to do the activity outdoors, try to do some social distancing, try to have people wearing face coverings where applicable,” Dr. Adalja says. Eating indoors around a dinner table is not recommended unless everyone present is part of the same quarantine pod.”Most of us anticipate we will see transmission events occur during Thanksgiving.”

Butler-Wu stresses the importance of taking precautions, because researchers still don’t know how COVID-19 affects patients months or years down the line, and SARS-CoV-2 acts differently than similar coronaviruses. “Testing is not a passport to acting like the Kardashians on the island. It’s not,” she says. “Using a negative test to decide that ‘none of us are going to wear a mask’ is a dangerous thing. No age group is immune from the potential consequences of this virus.”

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