About the Test
Purpose of the test
Most commonly 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 (proteins on the surface of the virus) 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 infection. If it is believed that you have delayed symptoms of 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.
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 they 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. 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 many 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 active or recent infection by antigen testing or PCR for 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.
At this time, SARS-CoV-2 antibody tests do not tell you if:
- You currently have COVID-19
- You have immunity that will prevent COVID-19
- You need a COVID-19 vaccine
- Your COVID-19 vaccine worked
When serology testing is conducted, it is important to consider the time it takes for the immune system to produce antibodies. It also can take days to weeks after the infection for your body to make detectable antibodies, 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 can I get a COVID-19 antibody test?
COVID-19 antibody testing usually occurs after being prescribed by a doctor.
The test requires a blood sample that can be taken in a doctor’s office, lab, or another medical setting. You can order a test online and have a sample collected at a local lab. Blood is drawn from a vein or taken with a prick of your fingertip. Analysis of the blood sample is 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?
While there have been at-home testing options available in the past, there are currently no FDA- approved at-home tests available in the U.S. However, with the rapidly changing landscape of the pandemic, this is likely to change.
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 if one is available.
Before the test
There is no required preparation for a COVID-19 antibody test. Before the test, though, 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. This 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 usually 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, so your test sample can be analyzed on-site. 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. False positive test results may occur due to cross-reactivity from pre-existing antibodies.
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 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.
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?
Testing for COVID-19 can involve several distinct types of tests. The table below provides an overview of 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 |
