Antibody Test

What is an antibody (serology) test?

An antibody test looks for antibodies in your blood. Antibodies are proteins your body makes to fight infection. Your immune system creates unique antibodies to respond to different unknown substances such as viruses, bacteria and allergens (tiny particles that cause allergies). Providers also call this test a serology test.

Healthcare providers use antibody tests to tell if you’ve had an infection or if you’ve been exposed to a specific virus. A more recent example of this is the antibody test for SARS-CoV-2 (the virus that causes COVID-19). If you test positive for COVID-19 antibodies, that means you’ve been exposed to that virus and your body created antibodies to fight it. Your immune system also develops COVID-19 antibodies after you receive the COVID-19 vaccine.

After a vaccination, infection, or exposure to infectious agents, it can take up to several weeks for your immune system to make antibodies. Antibody tests are not the same as diagnostic tests that check for an active (current) infection. These tests do not detect the infectious agent itself. They evaluate your body’s response to the virus.

When would an antibody test be needed?

You may need a COVID-19 antibody test if you:

• Had symptoms of COVID-19 but didn’t get tested while you were sick.
• Had symptoms but tested negative for the virus. In this case, your provider may use an antibody test about a week or two after you recover to confirm a diagnosis of COVID-19.
• Have lasting COVID-19 symptoms or complications of COVID-19 after an infection (long COVID or long-hauler COVID-19). These complications include multisystem inflammatory syndrome (MIS-C).
• In addition to COVID-19, healthcare providers use antibody blood tests to check for a wide range of diseases and disorders. These tests help providers diagnose disease by detecting antibodies to specific viruses and bacteria. Your provider uses antibody tests to look for:
• Autoimmune disorders such as Celiac disease and lupus.
• Bacterial infections, including Lyme disease, pertussis (whooping cough) and tetanus.
• Cancer, including multiple myeloma.
• Viruses, including HIV, chickenpox (varicella-zoster virus), mononucleosis (which results from the Epstein-Barr virus) and West Nile virus.

Providers also use antibody tests to evaluate you or your child for allergies. The tests can tell if your immune system created antibodies in response to various allergens. Providers call the response an allergic reaction. But some of these tests (especially antibody tests for food allergies) can produce a false-positive result. That means the results might be positive for antibodies, but you may not actually be allergic.

Who performs an antibody blood test?

A healthcare provider performs this test. You get the test at your doctor’s office, a laboratory or a special clinic.

What are the types of antibody tests?

Different serology tests detect different antibodies. Your body creates five main types of antibodies:

• Immunoglobulin A (IgA).
• Immunoglobulin D (IgD).
• Immunoglobulin E (IgE).
• Immunoglobulin G (IgG).
• Immunoglobulin M (IgM).

Consider the COVID-19 antibody test as an example of how the process works:

Most COVID-19 antibody tests look for IgM and IgG antibodies. Your body usually produces IgM antibodies first, as soon as you’re exposed to a virus like SARS-CoV-2. These antibodies fade away sooner than others and may not be detectable for very long.

IgG and IgA antibodies usually appear about a week to 10 days after you were exposed to the virus. Since IgG antibodies stay in your body longer, an antibody test may detect these antibodies for months or even years after a COVID-19 infection.

If I got a COVID-19 vaccine, will I test positive for antibodies?

COVID-19 vaccines (such as the mRNA vaccine) teach your body how to create antibodies that fight the virus. So, you might test positive for COVID-19 antibodies if you get an antibody test after your vaccine. But your results will depend on several factors, including when you get the test and what type of antibody test you get. Different antibody tests check for different types of antibodies.