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  • Also Known As:
  • COVID-19 Serology
  • Serological Test
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Test Quick Guide

COVID-19 antibody testing is a way of trying to determine if you have previously been infected with the SARS-CoV-2 coronavirus that causes COVID-19.

Antibody testing is done with a blood sample and is also known as serology testing. It can be performed in a laboratory or with on-site, point-of-care testing. Antibody testing may be used in patients with long-lasting or late-developing complications. It is also used in research to better understand the COVID-19 pandemic.

About the Test

Purpose of the test

The standard use of an antibody test for COVID-19 is to determine whether a person is likely to have had a prior infection with SARS-CoV-2.

Antibody tests are not used to screen for active COVID-19. Instead, the most common uses of this test include:

  • Testing in people with persistent symptoms of COVID-19: If you have had symptoms of COVID-19 for several weeks, it is possible that an active infection is no longer detectable by antigen or PCR tests. In these cases, an antibody test can help demonstrate that you had a prior SARS-CoV-2 infection which may explain your symptoms and support a diagnosis of COVID-19.
  • Testing in people with late-developing complications of COVID-19: Some health effects of COVID-19 can develop weeks or months after an infection. If it is believed that you have delayed symptoms of a coronavirus infection, an antibody test may help determine if you were infected before.
  • Epidemiological research: Antibody tests can provide useful information to better understand COVID-19. For example, serology testing can help estimate how many people have been infected. Antibody tests can also be used to try to determine how past infection affects the risk of developing COVID-19 in the future.

It is important to note that the Centers for Disease Control and Prevention (CDC) does not recommend antibody testing to try to demonstrate immunity to COVID-19 or response to vaccination. Antibody testing is not validated in these cases, so antibody tests should not be used to coordinate arrangements for workplaces or shared living environments like nursing homes or college dorms nor to dictate one’s level of COVID-19 precautions.

What does the test measure?

COVID-19 serology tests measure antibodies in the blood. Antibodies are proteins generated by the immune system in its response to pathogens such as viruses.

The body produces antibodies that are specific to SARS-CoV-2. Tests can look for types of antibodies known as immunoglobulins including immunoglobulin G (IgG), immunoglobulin M (IgM), and immunoglobulin A (IgA). These antibodies develop at different stages after infection.

While testing is possible for all three of these types of immunoglobulins, most COVID-19 antibody tests focus on IgG or the total number of antibodies. IgG antibodies take several weeks to develop but can last for several months. As a result, they are generally viewed as the most reliable indicator of a prior infection.

When should I get a COVID-19 antibody test?

COVID-19 antibody tests are typically only used in specific circumstances. Most often, the test is prescribed when you have symptoms that could be related to COVID-19, but the infection is believed to have occurred several weeks or months earlier. In these cases, you may have already tested negative for an active infection with SARS-CoV-2.

You may also get a serology test if you are taking part in a research study. In this situation, you will be advised about the details of the study’s purposes and procedures prior to testing.

Antibody tests cannot be used to show if you are immune to COVID-19. They also cannot prove whether vaccination was effective. Not enough is known about the relationship between antibody levels and immunity, and for this reason the CDC advises against using antibody tests in these contexts.

When serology testing is conducted, it is important to consider the time it takes for the immune system to produce antibodies. It often takes several weeks for antibodies to become detectable, so an antibody test too soon after infection may not be accurate. In addition, although antibodies have been detected for around eight months after infection in some people, they may last for a shorter period of time in others.

Finding a COVID-19 Antibody Test

How to get tested

COVID-19 antibody testing usually occurs after being prescribed by a doctor. It requires a blood sample that can be taken in a doctor’s office, lab, or other medical setting. Blood can be drawn from a vein or taken with a prick of your fingertip. Analysis of the blood sample can be done immediately on-site with point-of-care testing, or the sample can be sent to a laboratory.

Can I take the test at home?

At-home options for COVID-19 antibody testing are limited. The FDA has authorized a test that involves collecting a blood sample at home and sending it to a lab for testing. This home-collection kit is currently only available with a prescription.

How much does the test cost?

Several factors can affect the cost of antibody testing including where the sample is taken, whether it’s a point-of-care or laboratory-based test, and the type of technology used to analyze the sample.

The costs involved in testing can include technician fees for obtaining a blood sample, fees for analysis, and charges for office visits. These costs are often covered by health insurance if the antibody test is prescribed by your doctor.

Check with your doctor and insurance provider to find out about copays, deductibles, and any other charges if you have a COVID-19 serology test. If you are having testing done as part of a research study, ask the research team if there are any required out-of-pocket costs.

Taking a COVID-19 Antibody Test

Antibody tests require a blood sample. This sample can be taken by drawing blood from a vein in your arm or by pricking your fingertip to obtain a drop of blood. The test is usually done in a medical office or hospital but may be done with an at-home sample collection kit.

Before the test

There is no required preparation for a COVID-19 antibody test. Before the test, though, you should tell your doctor if you have had any recent symptoms of COVID-19 or if you have received a COVID-19 vaccine.

If you are taking a blood sample with an at-home kit, make sure to carefully review the instructions before getting started to ensure that you properly collect an uncontaminated sample.

During the test

If your test is being done with a blood draw, you will have an elastic band tied around your upper arm, and the inside of your elbow will be cleaned with an antiseptic pad. A needle will be inserted into the vein, a vial of blood will be drawn, and then the needle will be removed. The entire process usually lasts less than a few minutes during which there may be some temporary pain as the needle is inserted and withdrawn.

If you are having a fingerstick blood test, your fingertip will be cleaned with an antiseptic and then a very small needle will prick your finger to produce a drop of blood. The test lasts less than a minute. The fingerstick may cause a brief sting.

After the test

After blood is drawn with a needle, a bandage is applied, and you may need to apply light pressure for a few minutes to help prevent bleeding. There may be tenderness at the puncture site, and some light bruising may occur. You can usually return to normal activities once the test is complete.

With a fingerstick blood draw, a small bandage may be applied if necessary. Lasting effects are rare, and you can normally return to normal activities as soon as the test is over.

COVID-19 Antibody Test Results

Receiving test results

Many antibody tests are point-of-care tests, which means that your test sample can be analyzed on-site and without sending it to a laboratory. These are often rapid tests with results available in 30 minutes or less. If the test sample is sent to a laboratory, you should receive results within a few business days.

You may get your test results from your doctor or another health care provider who conducts a rapid point-of-care test. A test report may also be sent by mail or made available to you electronically.

Interpreting test results

Your test result is typically listed as either positive or negative. Positive means that antibodies to SARS-CoV-2 were found in your blood. Current tests do not usually provide a detailed list of the precise numbers of specific antibodies detected.

In general, a positive test result reflects a previous infection with SARS-CoV-2, but it is possible for a person who has never had COVID-19 to have a positive test. This is known as a false positive, and it can occur if antibodies to another type of coronavirus were detected by the test as antibodies to SARS-CoV-2.

Similarly, a negative test result does not assure that you have never had COVID-19. It is believed that antibodies wane over time, and people who had mild or asymptomatic cases of COVID-19 may develop fewer antibodies. Additionally, some individuals do not produce these types of antibodies after an infection, but still produce other immune cells in response to infection. Therefore a negative antibody test should not be used to rule out immunity.

It is important to talk with your doctor about how to interpret the result of your antibody test. Because of the possibility of a false positive or false negative test, your doctor considers your results within the context of your situation including your symptoms and the likelihood that you were previously exposed to SARS-CoV-2.

Are test results accurate?

There are different versions of antibody tests, and not all of them are equally accurate. In general, though, most authorized antibody tests provide dependable results.

While the test methods can reliably determine if antibodies are present, several factors can affect the accuracy of both the test and its interpretation:

  • Cross-reactivity: SARS-CoV-2 is one type of coronavirus. Other coronaviruses are common, and it is possible for the test to mistakenly identify antibodies to one of those coronaviruses as antibodies to SARS-CoV-2.
  • Test timing: It can take several weeks for antibodies to form, which means that testing too soon after infection may return a false negative result. In addition, antibodies decline over time, so testing too late may not correctly reflect whether you had a prior SARS-CoV-2 infection.
  • Vaccination status: Getting a vaccine for COVID-19 causes the body to produce antibodies to a specific part of SARS-CoV-2 known as its spike protein. In serology tests that look for these specific antibodies, vaccination may cause a positive result. The presence of antibodies to other proteins in SARS-CoV-2 may be an indicator of a past infection rather than a result of vaccination, so it is important to note which type of antibodies are being tested.
  • Test method and platform: Distinct technical methods for detecting antibodies can be used, and the choice of testing technology may affect the accuracy of your results.

Do I need follow-up tests?

Follow-up after antibody testing will vary based on the reason why the antibody test was performed. If you have ongoing or late-developing symptoms of COVID-19, you may have other tests that help monitor those symptoms and your overall health.

Questions for your doctor about test results

If you have had a COVID-19 serology test, the following questions may be helpful to review with your doctor:

  • What was my test result?
  • Does my result mean that I did or did not have COVID-19?
  • How confident are you in the test result?
  • Do I need any follow-up tests based on my test result?

Related Tests

Testing for COVID-19 can involve several distinct types of tests. The table below provides an overview of COVID-19 test categories and how and why they are performed:

COVID-19 Test Purpose Sample
Antibody Test Detect prior infection Blood sample
Antigen Test Detect current infection Nose swab
PCR and Molecular Tests Detect current infection Nose swab, throat swab, or saliva sample

The following sections provide more detailed information on how antibody testing is different from antigen and PCR/molecular tests for COVID-19.

How is antibody testing different from COVID-19 antigen testing?

Antibody testing typically looks for signs of a prior infection with SARS-CoV-2. In contrast, COVID-19 antigen tests look for signs of a current infection.

Antigens are proteins on the surface of the virus while antibodies are created by the immune system to help fight the virus. Antigens are detectable soon after infection when lots of the virus is present in the body, which is why they can detect active infections.

In addition, antigen tests are conducted with a sample taken from the nose while antibody tests are done with a blood sample.

How is antibody testing different from PCR and molecular testing for COVID-19?

PCR and other molecular tests are ways of finding active cases of COVID-19. This is a critical difference from antibody tests that try to detect past infection with SARS-CoV-2. Another difference is the kind of sample. Antibody tests use a blood sample, and a PCR is done on a specimen from the respiratory tract.

Other related tests

Sources and Resources

More information about SARS-CoV-2 and COVID-19 can be found in the following trusted resources:

Sources

A.D.A.M. Medical Encyclopedia. COVID-19 antibody test. Updated February 7, 2021. Accessed April 22, 2021. https://medlineplus.gov/ency/article/007773.htm

A.D.A.M. Medical Encyclopedia. COVID-19 virus test. Updated February 7, 2021. Accessed April 22, 2021. https://medlineplus.gov/ency/article/007769.htm

Caliendo AM, Hanson KE. COVID-19: Diagnosis. In: Hirsch MS, ed. UpToDate. Updated April 16, 2021. Accessed April 22, 2021. https://www.uptodate.com/contents/covid-19-diagnosis

Centers for Disease Control and Prevention. COVID-19 testing overview. Updated March 17, 2021. Accessed April 22, 2021. https://www.cdc.gov/coronavirus/2019-ncov/symptoms-testing/testing.html

Centers for Disease Control and Prevention. Interim guidelines for COVID-19 antibody testing. Updated March 17, 2021. Accessed April 22, 2021. https://www.cdc.gov/coronavirus/2019-ncov/lab/resources/antibody-tests-guidelines.html

Centers for Disease Control and Prevention. Nucleic acid amplification tests (NAATs). Updated April 16, 2021. Accessed April 22, 2021. https://www.cdc.gov/coronavirus/2019-ncov/lab/naats.html

Centers for Disease Control and Prevention. Self-testing. Updated April 15, 2021. Accessed April 22, 2021. https://www.cdc.gov/coronavirus/2019-ncov/testing/self-testing.html

Centers for Disease Control and Prevention. Test for current infection (viral test). Updated March 18, 2021. Accessed April 22, 2021. https://www.cdc.gov/coronavirus/2019-ncov/testing/diagnostic-testing.html

Centers for Disease Control and Prevention. Test for past infection. Updated February 2, 2021. Accessed April 22, 2021. https://www.cdc.gov/coronavirus/2019-ncov/testing/serology-overview.html

Centers for Disease Control and Prevention. Using antibody tests for COVID-19. Updated November 3, 2020. Accessed April 22, 2021. https://www.cdc.gov/coronavirus/2019-ncov/lab/resources/antibody-tests.html

Kim AY, Gandhi RT. COVID-19: Management in hospitalized adults. In: Hirsch MS, ed. UpToDate. Updated March 24, 2021. Accessed April 22, 2021. https://www.uptodate.com/contents/covid-19-management-in-hospitalized-adults

McIntosh K. COVID-19: Epidemiology, virology, and prevention. In: Hirsch MS, ed. UpToDate. Updated March 31, 2021. Accessed April 22, 2021. https://www.uptodate.com/contents/covid-19-epidemiology-virology-and-prevention

UpToDate. COVID-19: Questions and answers. Updated April 19, 2021. Accessed April 22, 2021. https://www.uptodate.com/contents/covid-19-questions-and-answers

UpToDate. Patient education: COVID-19 overview (the basics). Date unknown. Accessed April 22, 2021. https://www.uptodate.com/contents/covid-19-overview-the-basics

US Food and Drug Administration. Antibody (serology) testing for COVID-19: Information for patients and consumers. Updated July 29, 2020. Accessed April 22, 2021. https://www.fda.gov/medical-devices/coronavirus-covid-19-and-medical-devices/antibody-serology-testing-covid-19-information-patients-and-consumers

US Food and Drug Administration. Coronavirus (COVID-19) update: FDA issues emergency use authorization for the symbiotica COVID-19 self-collected antibody test system. Updated April 6, 2021. Accessed April 22, 2021. https://www.fda.gov/news-events/press-announcements/coronavirus-covid-19-update-fda-issues-emergency-use-authorization-symbiotica-covid-19-self

US Food and Drug Administration. Coronavirus disease 2019 testing basics. Updated April 7, 2021. Accessed April 22, 2021. https://www.fda.gov/consumers/consumer-updates/coronavirus-disease-2019-testing-basics

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