If You're Asymptomatic, This COVID Test Could Fail You
Research has found that this kind of test may give inaccurate results if you have no symptoms.
The country looks a lot different now than it did when the pandemic first hit, though case numbers are higher than ever. With the pandemic showing no signs of slowing down, people are relying on coronavirus tests to determine if they can see family and friends or go out into large crowds. And many have become reliant on rapid COVID tests, which are designed to give results within minutes rather than days. However, this COVID test may not be so accurate for everyone. In fact, a new study has found that a rapid COVID test might not give you correct results if you're asymptomatic. Read on for the truth about rapid test accuracy, and for more on the future of coronavirus, These 5 People Will Get the COVID Vaccine First, Dr. Fauci Says.
One rapid COVID test missed more than two-thirds of positive asymptomatic cases.
Researchers from the University of Arizona conducted a study on the rapid antigen test made by Quidel, as reported earlier this month by The New York Times. When testing asymptomatic patients or people who did not feel sick, the test only accurately detected 32 percent of the positive cases reported by a slower, lab-based PCR test.
In the study, researchers tested around 2,500 people from June to August. For the 1,551 people randomly selected with no symptoms, 19 tested positive with PCR tests. However, the rapid test only caught six of those cases. And for more on COVID spread, This Is When Someone Is Most Likely to Give You COVID, Study Shows.
But the rapid test accurately identified more than 80 percent of positive symptomatic cases.
Unlike asymptomatic cases, this rapid COVID test could detect more than 80 percent of coronavirus infections reported by the PCR test. Of the 885 people that had either experienced COVID-like symptoms or been exposed to the virus, 305 tested positive with the PCR test. The rapid test caught 251 of those, missing 18 percent.
"The data for the symptomatic group is decent," Jennifer Dien Bard, PhD, the director of the clinical microbiology and virology laboratory at Children's Hospital Los Angeles, who was not involved in the study, told The New York Times. "But to get less than 50 percent in the asymptomatic group? That's worse than flipping a coin." And for coronavirus symptoms to be on the lookout for, These 4 Easy-To-Miss Symptoms Could Mean You Have COVID, Experts Say.
This may be because rapid tests aren't necessarily meant for asymptomatic patients.
According to The New York Times, the U.S. Food and Drug Administration (FDA) only authorizes the use of Quidel tests for people with symptoms, yet the use of rapid tests for asymptomatic people has been "strongly encouraged by the federal government." Even the Centers for Disease Control and Prevention (CDC) cautions the public against using a negative result from a rapid COVID test as their only source of judgment. The CDC says there is still only "limited data to guide the use of rapid antigen tests as screening tests on asymptomatic persons to detect or exclude COVID-19, or to determine whether a previously confirmed case is still infectious." And for more on the limitations of this form of testing, discover What the White House Outbreak Has Taught Us About Rapid COVID Tests.
Researchers also think these results may mean asymptomatic patients are not as infectious.
David Harris, PhD, a stem cell researcher and an author on the study, said that the antigen tests may have missed certain asymptomatic patients because they were carrying too little of the virus to spread to someone else. The CDC says rapid antigen tests "detect the presence of a specific viral antigen," meaning if they can't detect enough coronavirus material to give a positive result, there may not be enough of a viral load to infect others.
According to Harris, researchers weren't able to grow the live coronavirus from samples of volunteers who had C.T. values above 27. And of the 13 asymptomatic patients missed by the Quidel test, 12 had C.T. values in the 30s. "If I don't have live virus, I am not infectious at all," Harris explained to The New York Times. And for more up-to-date information, sign up for our daily newsletter.
But other experts say that there is still not enough research to determine asymptomatic people's infectiousness.
Omai Garner, PhD, the associate director of clinical microbiology in the UCLA Health System, who was not involved in the study, told The New York Times that there is no proof that failing to grow the coronavirus from a person's sample means they are not contagious. And other experts noted that the University of Arizona did not track coronavirus transmission from the participants, so they can't make conclusions about the virus' spread.
Either way, people should not rely on rapid antigen tests when it comes to negative results. Susan Butler-Wu, PhD, a clinical microbiologist at the University of Southern California, who was not involved in the study, told The New York Times that people, especially those with known exposure to the coronavirus, should still get more precise and reliable PCR tests. And if you're worried about getting sick, This Is the Easiest Way to Tell If You've Been Exposed to COVID.