What Is The Coronavirus Antibody Test?

Last week, the FDA approved a new test under an Emergency Use Authorization, in response to the coronavirus pandemic. It's not necessarily meant to determine whether someone has COVID-19, though. Instead, it detects whether someone has already had it — by measuring their antibody levels.

This type of antibody test is already being used in other countries, including China, says Shawn Nasseri, MD, who practices in Beverly Hills. This is the first to be approved for use in the U.S.

Here's everything you need to know about the new test, including how it works and why it's important.

Quick biology lesson: Antibodies are the blood proteins the body produces in response to bacteria or, viruses, and other toxins, according to MedlinePlus. They're thought to help the body neutralize these foreign substances. So if you get the flu one year, your body produces antibodies that are specific to that strain of flu.

If COVID-19 antibodies are present in someone's blood, that would indicate that (1) the person had previously had COVID-19, and (2) the person may have some immunity to it.

The recently approved test, also called a serological test, analyzes a blood sample taken from a finger prick. It picks up two types of antibodies: immunoglobulin M, which is created when the body first reacts to a toxin, and immunoglobulin G, which is the kind that makes you immune to getting it again.

The COVID-19 antibody test is meant to deliver results in about 15 minutes.

Knowing who has had COVID-19 and who likely immune to catching it again has many benefits. "If [a person] have a robust response, then you know that they're likely to be immune [to the virus]. They could be the person who goes out for groceries every week, who checks the mail and does everything critical," says Dr. Nasseri. "They also could be the early people to return to somewhat normal activity. More importantly, they could be identified as potential donors for plasma for people who have severe COVID-19."

Although promising, this test does have drawbacks. There's a 10 to 30% chance that the antibodies it detects may be from another cold or infection you previously had, not COVID-19 in particular, says Dr. Nasseri. (Remember that time Kim Kardashian tested positive for lupus antibodies, but didn't have lupus? It's kind of like that.)

What's more, it may be possible to get the virus again, despite having antibodies in your blood. The new test looks only for the presence of the antibodies; not whether they're functional, Dr. Angela Rasmussen, a virologist at Columbia University in New York, told The New York Times.

The test "should not be used as the sole basis to diagnose COVID-19," the FDA cautioned in a statement released on April 7. When you first catch the virus and the body is still building its immune response, these antibodies may not be detected. "This limits the test’s effectiveness for diagnosing COVID-19," the FDA said.

Still, in the future, this kind of antibody test could be used to help determine if certain individuals are no longer susceptible to infection and can return to work, according to the FDA. These test results can also aid in determining if someone can donate plasma, which may serve as a possible treatment for those who are ill from COVID-19. 

The company behind the test, Cellex, is now allowing healthcare providers to order the test online through their website.