FAQ: Antibody Testing

There’s been a lot of buzz in the news about the need for antibody testing during the coronavirus disease 2019 (COVID-19) pandemic. The idea is that antibody tests, which look for evidence that the body has already fought off the infection, could identify people who have developed immunity to the virus and may be able to reduce physical distancing measures.

Unfortunately, it’s not that simple yet. Antibody testing for COVID-19 is just getting started. While several tests are available with and without emergency use authorization from the Food and Drug Administration, there are questions about their reliability, and even about whether COVID-19 is like other viruses in that past infection generally confers future immunity.

While we wait for widespread availability of antibody testing, it’s helpful to understand how it works.

UNC microbiologist Premkumar Lakshmanane, PhD, has worked with other researchers at the UNC School of Medicine to develop improved antibody testing to fight the Zika virus. We talked to Dr. Lakshmanane to learn how antibody testing can help fight viruses.

What Are Antibodies?

Antibodies, also known as immunoglobulins, are proteins that your body’s immune system makes to attack foreign substances such as viruses and bacteria. These foreign substances are called antigens. Just as there are a large number of antigens, there are a vast number of antibodies that attack different antigens.

When an antigen enters your body—for example, when you get the flu—a white blood cell called a lymphocyte detects the unfamiliar agent and produces antibodies that are specific to that antigen. Then the antibodies help clear the antigen from your body. Imagine soldiers deployed to fight off an enemy who has crossed enemy lines.

“The antibodies develop as an immune response to an infection,” Dr. Lakshmanane says.

Like pieces of a puzzle, each antibody has a uniquely designed shape to recognize a specific antigen. Once the antigen is destroyed, you start to feel better because your body is done fighting the infection.

After you have defeated the antigen—you have recovered from that virus—you usually do not catch it again because your body created memory cells that are specific to that antigen. That’s why you typically don’t get repeat viral infections. If you are exposed to it again, your body rapidly makes the correct antibody, and the antigen is destroyed before you even feel symptoms of the disease.

“If you have the antibodies to a particular antigen in your blood, it lowers your risk of reinfection,” Dr. Lakshmanane says.

Keep in mind that it takes time for the body to develop antibodies to attack the specific antigen, and that’s why you feel sick for a few days or even a week when you get the flu.

After approximately 10 days, the antibodies should be at work against the antigen, which means your body has fought the infection, Dr. Lakshmanane says.

What Is Antibody Testing?

Antibody testing, also called serology testing, seeks to determine if a person has been exposed to a specific antigen, such as a virus. It is done using a blood sample, which is usually obtained by a finger prick or blood draw.

“The serology test is not looking for the virus,” Dr. Lakshmanane says. “It is trying to determine whether your immune system has responded to an infection caused by the virus.” In other words, it is looking for the antibodies that fought the virus.

To do this, researchers will design specific parts of the virus that correspond to the place where antibodies attack it—the parts of the puzzle that fit together. They then test it.

If an antibody test is negative, no antibodies were detected. A positive antibody test means that the body has been exposed to the virus being tested.

Why Is Antibody Testing Important?

Antibody testing has been used for many years for a variety of reasons such as to diagnose some infections, cancers, allergies and autoimmune disorders such as hyperthyroidism and hypothyroidism. For example, the test to check whether a pregnant woman is at risk of or immune to rubella (German measles) is called a rubella antibody test.

Now, researchers say antibody testing could be the key to determining how widespread COVID-19 is, which will help identify who might now be immune to novel SARS coronavirus, the virus that causes COVID-19, because they have already had it, regardless of whether they had symptoms or not.

The immediate goal of an antibody test for COVID-19 is to establish if healthcare and other essential workers are still at risk of infection. This information also can be used to estimate infections among broader communities, which many are hopeful can help determine timelines for reopening businesses and lifting stay-at-home orders.

For the latest information on COVID-19, visit the CDC website and the UNC Health COVID-19 Resources page, and follow UNC Health on Twitter, Facebook, Instagram and YouTube.