How Reliable Are COVID-19 Antibody Tests?

The FDA approved the first coronavirus test that looks for antibodies in the blood, but doctors say we should be cautious.
Posted at 11:22 AM, Apr 06, 2020

The FDA approved a coronavirus test that looks for antibodies in the blood — a major step forward in the effort to identify people who may have some immunity to the coronavirus.  

It’s called a serology test and is different from the nasal swab tests being used now — those tests are designed to find out if you have the virus. Antibody tests are designed to find out whether your body has built up defenses against the virus.

That’s important because researchers believe that past exposure to the coronavirus may protect people from getting COVID-19 again.

"The serology measures an antibody in the blood that has taken time to accumulate. So the antibody response can take weeks to begin to develop. And so measuring the antibody blood of someone indicates that they may have had the illness up to many weeks ago, and some antibodies to some infections can persist for the lifetime of an individual," Dr. Ben Singer, a pulmonary and critical care specialist at Northwestern Medicine told Newsy.

The FDA granted emergency use authorization to a manufacturer called Cellex. The test requires blood to be collected from a vein and can only be performed in a certified lab.

It’s not the only antibody test out there. Singaporeand China have already been antibody testing. The U.K. has its own test and recently ordered 3.5 million kits to be distributed by Amazon and pharmacies around the country in just a matter of days.

Here in the U.S., from Mount Sinai to the Mayo Clinic, some hospitals have developed antibody tests for COVID-19

The serological tests aren’t perfect, though. False positives are possible because a person could have antibodies from other coronavirus strains. Even the FDA says “Cellex's labeling notes that test results from this serology test should not be used as the sole basis for diagnosis.” More than a dozen companies making antibody tests are allowed to distribute them to hospitals and doctors’ offices, but have to carry disclaimer statements that read: “This test has not been reviewed by the FDA.” Accuracy and reliability won’t be ensured without validation and experience.

We also need to keep in mind that while ever-present, COVID-19 is still new, so we don’t have data on how long immunity may last. Experts say the virus seems to be mutating slowly, so it shouldn’t pose yearly issues like the flu. But with only studying it for three months, there’s still a lot we don’t know, like if antibodies would protect someone like a nurse who's been exposed to a large quantity of the coronavirus. 

Dr. Singer says no medical test will be perfect, but that people should exercise caution if they do get antibody tested in the weeks to come as these tests are expected to become more available. 

"We have almost no test in medicine that gives zero false positives and zero false negatives. That's just the nature of medical testing. And so as we learn more or about these assays and learning how they're used appropriately, I agree that caution is warranted until we have data to really guide us," Dr. Singer said.

Antibody serum is also being looked at in several clinical trials as a short-term treatment option. They’re looking to see if giving infusions of survivors' antibody-rich plasma to newly ill COVID-19 patients would boost their own bodies' attempts to fight off the virus.