What Is an Antigen Test?

Understanding a new type of coronavirus test authorized by the FDA

Emily Mullin
Medium Coronavirus Blog

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A Sofia machine, made by Quidel Corporation, which is used to run the company’s 15-minute Covid-19 antigen test.
A Sofia machine, made by Quidel Corporation, which is used to run the company’s 15-minute Covid-19 antigen test. Photo: Quidel

A new category of coronavirus tests is here. On May 9, the U.S. Food and Drug Administration authorized the first antigen test to diagnose Covid-19, made by Quidel Corporation, a San Diego-based company that develops medical testing. Former FDA commissioner Scott Gottlieb told CBS’s Face the Nation that the technology behind it is “a real game changer.”

So what is an antigen test and how does it work?

Antigens are molecules on the surface of a virus or other germs that cause the body to produce an immune response. They can also come from substances in the environment like chemicals or pollen. A viral antigen test is designed to look for fragments of antigens from a virus, unlike most diagnostic tests, which look for the presence of the virus itself. Quidel’s test looks for antigens found on SARS-CoV-2, the virus that causes Covid-19, using a nasal swab. If you take the test and the results come back positive, it means that you are currently infected with Covid-19.

One of the benefits of antigen tests is that they provide rapid results, which means they could be done in emergency rooms or doctor’s offices to quickly determine whether someone is sick with Covid-19. Quidel’s test takes just 15 minutes to return results.

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Emily Mullin
Medium Coronavirus Blog

Former staff writer at Medium, where I covered biotech, genetics, and Covid-19 for OneZero, Future Human, Elemental, and the Coronavirus Blog.