Nick Kanaan, Ph.D.:
Simply put, antibody tests are set up to show a positive signal if a patient’s blood sample contains antibodies against COVID-19. [Scroll down for a definition of antibody.]
Basically, the parts of the virus that the person’s antibodies bind to are used as bait to catch the person’s antibodies that specifically target COVID-19. Then the caught antibodies are detected, producing either a positive signal if indeed COVID-19 antibodies are present, or negative if the blood did not contain COVID-19 antibodies.
The sensitivity and specificity can vary from test to test depending on the platform used. For example, antibody tests that resemble pregnancy tests (typically called lateral flow tests) are generally less sensitive than other, more sophisticated forms of antibody tests, but they are very rapid and can be done on-site. More sophisticated forms of antibody tests are more sensitive and specific, but they take longer and typically require some specialized equipment. Depending on the antibody that the test detects, the sensitivity and specificity can vary from a moderate (~70%) to high (~100%) levels.
A large number of tests have hit the market recently, and this is a very active area of on-going research. Ideally, an antibody test will be relatively rapid and easy to implement, while also showing high sensitivity and specificity.
Antibody tests will likely be an instrumental component of the strategy for COVID-19. One difference between antibody tests and the nasal swab/saliva tests that detect the virus’s genes is that the antibodies will likely maintain a presence for some amount of time after the virus is gone. This can help to identify people that were infected. The exact amount of time that antibodies are present post-infection is still actively being investigated by many groups and some recent research suggests they may not remain in the body as long as initially thought. Much of our understanding of COVID-19 continues to shift as more research is being conducted daily across the globe.
What is an antibody?
Nick Kanaan:
An antibody is a protein (also referred to as an immunoglobulin) found in the blood that the body’s immune system creates to grab onto foreign substances, such as viruses like COVID-19, and help remove them from the body. Antibodies against COVID-19 are important in two ways. First, they are part of the body’s natural response to help fight off the infection of COVID-19. Second, they can be used to test whether a patient was infected with COVID-19 since antibodies stick around in the body even after the virus has subsided. The second feature is one of the advantages of serological or blood-based COVID-19 antibody tests.
Further clarification on antibody tests:
An antibody test is a screening for things called antibodies in your blood. Your body makes these when it fights an infection, like COVID-19. The same thing happens when you get a vaccine, like a flu shot. That’s how you build immunity to a virus.
You may also hear it called a serology test.
The antibody test isn’t checking for the virus itself. Instead, it looks to see whether your immune system -- your body’s defense against illness -- has responded to the infection.
Resources:
Flawed COVID-19 antibody tests shipped without FDA review: A 60 Minutes investigation has found that federal officials knew many COVID-19 antibody testing kits had flaws, but allowed them to enter the U.S. market. June 28, 2020
What to know before getting a COVID-19 antibody test: Doctors tell 60 Minutes that patients should get multiple antibody tests to ensure an accurate result, but testing positive for antibodies may not mean prolonged, or any, immunity. June 28, 2020
CNN Health: Beware of fake coronavirus antibody tests, the FBI warns. June 29, 2020
New Cochrane review assesses how accurate antibody tests are for detecting COVID-19. June 25, 2020
The Guardian: I'm a viral immunologist. Here's what antibody tests for Covid-19 tell us. June 25, 2020
The Guardian: Antibody test accuracy lower during first 14 days of Covid-19 symptoms. June 25, 2020
The Telegraph: Coronavirus antibody tests could do more harm than good by offering false hope, review warns. June 25, 2020
Reuters: Many studies of COVID-19 antibody test accuracy fall short: review. June 25, 2020
FBI.gov: FBI warns of potential fraud in Covid-19 antibody testing. June 26, 2020