COVID-19 often causes mild symptoms similar to those of the common cold and flu. Infection with the novel coronavirus can even come with no symptoms at all. That has some people wondering if they were infected and didn’t know it. Antibody testing – a test that looks for an immune response to a past infection – seems like it could provide the answer. But can it?
Here’s what you need to know about the COVID-19 antibody test:
What’s the difference between a PCR test and a serology test?
There are two kinds of COVID-19 tests available: tests to determine if you have an active infection (PCR or antigen tests) and tests that tell if you’ve had a previous infection. The antibody test (serology test) is a blood test that looks for a previous infection. It identifies antibodies that signal your immune system to respond to the novel coronavirus.
How soon after COVID-19 do you have antibodies?
Your body makes multiple types of antibodies (proteins that fight specific germs) when you have an infection. “The most common antibody that we look for with testing is called IgG,” says Omai Garner, PhD, director of clinical microbiology for UCLA Health. “Its presence is usually associated with immunity. Tests can detect the IgG antibody for COVID-19 three weeks after infection.”
But not everyone who’s been exposed to the virus develops IgG (Immunoglobulin G) antibodies. That’s because your immune system has two levels of defense:
Innate immune system
This part of your immune system is the first line of defense. It identifies foreign invaders and destroys them. If germs are killed at this point, no antibodies are made.
Adaptive immune system
This is the second tier of the immune system. If germs get past the front line, the adaptive immune system moves into action. This part of your immune system is responsible for germ-killing tactics such as raising a fever and making antibodies.
How does the COVID-19 antibody test work?
A COVID-19 antibody test is done by drawing blood or by pricking your finger. The sample can be tested on the spot or sent off to a laboratory, where technicians analyze the blood for COVID-19 antibodies. You receive results within about a week. A positive result generally means you have antibodies.
How reliable is the antibody test for coronavirus?
It’s possible to receive a false positive from a COVID-19 antibody test. That means you really don’t have the antibodies even though the test says you do. This can happen because of how the test is interpreted or because of the test itself. There are several different antibody tests on the market. Some are more accurate than others.
“Very few of the finger stick blood tests are reliable,” says Garner. “They’re typically interpreted by non-lab personnel, who may read them incorrectly. Also, many of these tests have lower sensitivity and accuracy. You’ll usually get better results with a blood draw test that uses a centralized laboratory for analysis. The test should also have emergency use authorization (EUA) from the Food and Drug Administration.”
Who should get the antibody test for coronavirus?
You are a good candidate to be tested if you fall into a category of people who have higher rates of exposure, such as those who:
- Previously tested positive for an active infection
- Had COVID-19 symptoms, but didn’t get tested for the active infection
- Are frontline workers such as firefighters, police officers and health care workers
Can you get COVID-19 again if you have the antibodies for it?
Experts don’t know for sure if antibodies offer protection against reinfection, or for how long. There are some disease antibodies, such as those for hepatitis B, that protect you for decades. But there are others, such as whooping cough, that only protect you for a couple of years.
“We don’t have a definitive answer about COVID-19 immunity yet,” says Garner. “Good data suggests that once you have the antibodies, you likely have some short-term protection. But since there is a level of uncertainty, it’s important to continue practicing infection prevention measures.”
Even if the test indicates you have COVID-19 antibodies, you should continue to:
- Avoid gathering in groups
- Avoid touching your face
- Stay 6 feet apart from people you don’t live with
- Wash hands frequently with soap and water for at least 20 seconds (or use hand sanitizer with at least 60% alcohol content)
- Wear a face covering when out in public