I. What is antibody testing for COVID-19?

Currently, there are two types of COVID-19 testing available. Viral tests diagnose current COVID-19 infections by testing a sample of mucus collected from a patient’s nasal passage.

The other type of test is an antibody test (also known as a serology test), which detects the presence of antibodies in a person’s blood, indicating that they were previously infected with COVID-19.

According to the Centers for Disease Control and Prevention (CDC), “Antibodies are proteins that help fight off infections and can provide protection against getting the disease again.” COVID-19 antibodies may be present in an individual’s blood even if they did not display any symptoms of the disease. The presence of these antibodies may give an individual some immunity against reinfection. However, because of the newness of this disease, no one knows for sure how much immunity COVID-19 antibodies provide, and how long this immunity lasts.

II. How is COVID-19 antibody testing conducted?

Antibody tests are conducted by collecting a blood sample. The sample is then tested for one or both kinds of COVID-19 antibodies — IgM antibodies, which appear early in an infection, and IgG antibodies, which show up later.

At this time, COVID-19 antibody tests must be performed by a healthcare provider. There is typically a waiting period for test results, which can range anywhere from a few days to a week or more. When you go to have your sample collected, your healthcare provider or the testing site should give you a timeframe for receiving your results.

III. How can you get a COVID-19 antibody test?

As with COVID-19 viral testing, state and local governments are coordinating the administration of antibody tests. If you are seeking a COVID-19 antibody test, you should start by contacting either your primary healthcare provider, or your state or local health department. They will help you determine whether you qualify for an antibody test, and if so, where you can obtain a test. Please note that sites that offer viral testing do not necessarily offer antibody testing as well.

Those seeking COVID-19 antibody tests should beware of fraudulent tests. The FBI recently issued a warning about fraudulent tests that scammers are using as a way to steal consumers’ private information. The FBI urges individuals to check the FDA’s website to confirm that a test is approved, and only share health information with trusted medical professionals.

IV. How accurate is COVID-19 antibody testing?

Antibody tests are not always 100 percent accurate. There are a few key factors that affect the accuracy of these tests:

  • Timing: According to the CDC, COVID-19 antibodies typically appear 1-3 weeks after the onset of infection. However, this timeframe can vary. If an individual is tested while they have an active COVID-19 infection, or before their body has started producing antibodies at detectable levels, their antibody test will come back negative, indicating that they do not have COVID-19. Conversely, there are still questions about how well serology tests can detect antibodies if a test is administered more than five weeks after the onset of symptoms, because it is not yet known with certainty how long COVID-19 antibodies remain in a person’s system.
  • Sensitivity: Even if an individual was infected with COVID-19, it is possible that their immune system did not produce enough antibodies to be detected in a serology test. Researchers suspect that this may be the case in children and those who are asymptomatic or only have mild symptoms. In this situation, a serology test could return a false negative.
  • Specificity: COVID-19 is just one of many viruses belonging to the coronavirus family. These types of viruses are also responsible for mild illnesses, like the common cold, in addition to the current, deadly COVID-19 illness. Therefore, it is possible for a COVID-19 serology test to mistakenly identify antibodies from other types of coronaviruses for COVID-19 antibodies. This would mean that, although a patient has coronavirus antibodies, they do not have antibodies specifically for COVID-19, and likely were not infected with the disease.

V. What should you do if you test positive for COVID-19 antibodies?

If you test positive for COVID-19 antibodies, the CDC recommends that you talk to your healthcare provider about what your test results mean, and what your next steps should be. Your healthcare provider may encourage you to take a second test to confirm the accuracy of your test results.

Even if you do test positive for COVID-19 antibodies, and confirm that you were infected and have recovered, you should still behave with caution. It is still unknown how long antibodies last, and how much protection they will provide against re-infection. Therefore, you should still take precautions, like wearing a mask, social distancing, and washing your hands frequently, to protect against further infection.

You may also want to consider donating plasma. Researchers are collecting and testing convalescent plasma as part of the effort to better understand COVID-19, and develop treatments for the disease.

If you test negative for COVID-19, it most likely means that you either did not have the disease, or you are currently infected and your immune system has not yet started producing antibodies. You may want to consider getting a diagnostic test to check whether you are currently infected. If a diagnostic test confirms that you have an active COVID-19 infection, you should seek treatment, and take steps to protect others, including self-isolating. If you do not have an active or past infection, you should take steps to protect yourself against contracting COVID-19, including practicing physical distancing whenever possible, wearing a mask in public places, and frequently washing your hands.

VI. Additional Resources

Name Website Summary
Centers for Disease Control and Prevention (CDC) https://www.cdc.gov/coronavirus/2019-ncov/index.html The CDC is the United States’ leading national public health organization. Its mission is to protect public health and safety through the control and prevention of disease, injury, and disability in the U.S. and abroad.
World Health Organization (WHO) https://www.who.int/ A specialized agency of the United Nations, WHO is responsible for international public health. Headquartered in Geneva, Switzerland, it has field offices worldwide.
Association of Public Health Laboratories (APHL) www.aphl.org The APHL is a nonprofit organization in the United States that represents laboratories that protect public health and safety.

VII. Sources