The FDA issued an emergency use authorization for a COVID-19 antigen test on Friday. Joining PCR and antibody testing, antigen tests are one of three FDA-approved tests for the novel coronavirus. Nate Favini, MD, MS, chief medical officer at Forward, explains that antigen tests could be a game-changer.
“The biggest thing we need to get the country back to normal, or at least toward normal, is that we just need really widely available testing,” says Dr. Favini. “Many of us in the medical community and the public health community have been saying for months that we just need to scale up testing in a really dramatic way. To the degree that this is an easier test to scale, it’s going to be helpful in getting testing available to more and more people.”
Rapid flu and strep tests, explains Dr. Favini, are examples of commonly used antigen tests, which identify any substance that causes your body to create antibodies to try and fight it off. Antigen tests employ technology readily available in most doctor’s offices, using samples collected from nasal swabs to identify fragments of protein found on or within the virus. The antigen test the FDA just approved for COVID-19 is manufactured by the Quidel Corporation. As of right now, the test is authorized to be run in facilities with the appropriate instrument provided by the same company, but as more companies release tests, more testing centers will be authorized to run COVID-19 antigen tests.
Rebecca Dutch, PhD, a virologist at the University of Kentucky’s College of Medicine, explains that antigen tests and PCR tests are both used to determine if a person is currently sick, while antibody tests can see if someone has been exposed. An antigen test is like the inverse of an antibody test, she says.
“The PCR test is what’s generally used now to look for active infection, and that’s looking for viral RNA,” says Dr. Dutch. An antibody test uses antigens to see if a patient’s blood contains antibodies that bind to the antigen; antigen tests use antibodies to see if the antigen is present in the patient’s nasal cavity.
A benefit of antigen tests is that they’re faster and cheaper than PCR tests. To run a PCR test, the RNA has to be replicated, which can take three to four hours. Antigen tests just look for a protein that’s already there and can be done in minutes. But a downside is that antigen tests aren’t as sensitive as PCR tests, says Dr. Favini. To ensure accuracy, the FDA is requiring negative antigen tests to be confirmed by a PCR test.
“One of the main advantages of an antigen test is the speed of the test, which can provide results in minutes. However, antigen tests may not detect all active infections, as they do not work the same way as a PCR test,” reads a statement from the FDA. “This means that positive results from antigen tests are highly accurate, but there is a higher chance of false negatives, so negative results do not rule out infection.”
While she’s unsure if this rule will stand forever, Dr. Dutch say it’s especially important while the medical community vets antigen test accuracy. COVID-19 PCR tests have been used enough for doctors and scientists to trust their accuracy, she says.
In the past few weeks, we’ve watched the tumultuous journey of antibody testing, which Dr. Dutch says is par for the course with any new treatment. Certain tests are more accurate than others, and we’ll likely see a similar situation happen with antigen tests, says.
“If you look at our clinical testing labs across the nation they have a long history of carefully evaluating everything to make sure it’s accurate enough, and they expect that new things rolling out have to be run through all sorts of additional checks,” she says. “Because so much is being written about everything even things that haven’t had a chance to be checked out are being written about on the front page of a major newspaper it just means that patients are now weighing in on it. And they’re more surprised that this is not a perfect process.”
It may be discouraging to see that antigen tests aren’t perfect, but they can still make a huge difference in the fight against COVID-19.
“A test doesn’t have to be perfect to make an impact on public health,” he says. “Even if you have a test that’s 80 percent accurate, if you test everybody on a weekly basis, you’ll catch enough cases and keep people home so that you can really suppress the transmission of the virus. Having a test like this which is cheaper and which gets testing out into more clinics and into more locations will help us identify cases and prevent the virus from spreading.”
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