Antibody Tests Can Be Inaccurate: How To Really Tell If You've Ever Had COVID

While the World Health Organization officially declared COVID-19 a pandemic1 on March 11, 2020, many believe the virus made its way stateside much earlier. In fact, the very first case of COVID-19 in the United States was confirmed on January 21, 20202. Considering the shaky timeline, the thought might have crossed your mind once or twice: Could I have had COVID before proper testing was available? 

"Think of your immune system not as a black-and-white switch but as an army of super-soldiers," he explains. "You've got your Army, your Navy, your Air Force, the Marines. They all have their own weapons; they all have their own skill set." 

In terms of what that looks like in your body, let's break it down: The fluid in your nose, mouth, and even eyes is packed with antibodies, says Li, which act like a first line of defense when they come into contact with viruses. "These are called IgA," says Li, or immunoglobulin A3. "They'll block a lot of viruses, and your body just sweeps them up and gets rid of them." Example: When you blow your nose into a tissue, the viruses will get swept out along with your mucus. 

But if the virus manages to sneak its way in, other super-soldiers must get to work: "And that's not just the generic antibodies," says Li. "It's other parts of your innate immune system that have to look at the invader. They've got to conduct surveillance... They send some troops out to take a closer look at it. They size it up. They take a picture of it and send it back to the home team to say, 'You know what? This doesn't look too good. I think we need to be able to mount a response.'"

Those soldiers—the ones who take snapshots of viruses who sneak past the first antibody system—are called T-cells. Says Li, whenever there's a "bad guy" who managed to get past the first line of defense, your T-cells memorize the virus so they can flag it to other parts of your immune system when it needs to warrant a response. "They put it in the iCloud of your immune system," he notes. 

All that is to say: A T-cell test may offer more accurate results than an antibody test since the T-cells will remember the virus as soon as it comes into contact with it. Meaning, if you've ever been infected with COVID, your T-cells will know.  

Whereas, "You'll only catch the antibodies against the virus for a window of time when there are enough made," says Li. "And then after a while, the antibodies will trail off." Those T-cells, though, will always have a fingerprint of the virus, whenever it was able to sneak its way inside.