Unlike commonly available coronavirus tests that use polymerase chain reaction, or PCR, antigen diagnostics work by quickly detecting fragments of virus in a sample. The newly approved Quidel test will rely on specimens collected from nasal swabs, according to the F.D.A., and they can only be processed by the company’s lab instruments.
“Diagnostic testing is one of the pillars of our nation’s response to Covid-19, and the F.D.A. continues to take actions to help make these critical products available,” the agency said in a statement on Saturday. “One of the main advantages of an antigen test is the speed of the test, which can provide results in minutes.” The F.D.A. said it expects to grant emergency clearance for other antigen tests in the near future.
A shortage of coronavirus tests in the United States has hampered efforts to contain the pandemic, and has limited the capabilities of states seeking to ease the lockdowns and social distancing measures that have throttled the nation’s economy.
Although antigen tests are extremely accurate in detecting positive infections, they cannot detect all active infections and they have a higher chance of false negatives than PCR tests. Positive test results may also need to be confirmed with the slower but more accurate PCR test, which relies on detecting the presence of genetic material.
Experts said the approval of an antigen test for Covid-19 would boost testing efforts by giving medical workers and health authorities an inexpensive tool for mass rapid testing. Further developed, antigen tests also hold potential for use at home, in the manner of a home pregnancy kit.
“I am very enthusiastic about antigen testing because of its ability to be scaled up to millions of tests a day, and because it has a much more rapid turnaround,” said Dr. Ashish Jha, director of the Harvard Global Health Institute. “A lot of us have been looking forward to this moment.”
Dr. Jha said he still had questions about the sensitivity and specificity of the test. He noted that even an antigen test that produces false positives is preferable to one that results in false negatives, because infected people given a negative result could unknowingly spread the virus to others.
“It’s ideal to have low false positives and false negatives, but usually you’re trading off between the two,” Dr. Jha said. “The reason you’re wiling to live with more false positives is you want to be able to screen people, and if they are negative you want to feel confident that they are truly negative.”