COVID-19 Antibody Test FAQ
About the antibody test
On May 21, our internist, Amanda Carmel, MD led a 30 minute discussion on the current state of COVID-19 antibody tests and what is available to our members. Watch here or read the details below.
What is the SARS-CoV-2 (COVID-19) antibody test?
The SARS-CoV-2 antibody test detects the presence of antibodies to SARS-CoV-2, the virus that causes COVID-19. Antibodies are proteins produced by the body’s immune system in response to an infection. Antibody tests, or serology tests, are often used as evidence of a past infection. There are several types of antibodies, including IgA, IgM, and IgG. Most antibody tests for SARS-CoV-2 detect the presence of IgM and/or IgG antibodies in the blood. However, some antibody tests, such as the one developed by our affiliate Mount Sinai, are able to detect both the presence and amount of antibodies in the blood.
Can antibody testing be used to diagnose COVID-19?
Antibody tests should not be used to diagnose COVID-19. Antibody tests help determine if a person has developed antibodies to SARS-CoV-2. It can take several weeks to develop antibodies, and not everyone who has been exposed to the virus may develop antibodies. Therefore, a negative antibody test does not rule out COVID-19. The PCR diagnostic test should be used to identify people who are actively infected with the virus. If you currently have symptoms of COVID-19, such as fever, cough, shortness of breath, chills, muscle pain, sore throat, or new loss of taste or smell, we recommend that you speak with your provider right away. Contact our Personal Health Navigators to be connected to a provider.
Who should get the antibody test?
The test is generally intended for people who either have had a positive test for COVID-19 and have recovered, or who think they were exposed to COVID-19 and no longer have symptoms or were asymptomatic.
Comparison of tests
Which antibody tests have been authorized for use by the US Food & Drug Administration (FDA)?
There are currently over 280 antibody tests on the market, but only some, including one developed by our affiliate Mount Sinai, have been authorized for use under the FDA’s Emergency Use Authorization (EUA).
For a list of tests that have been authorized by the FDA, please refer to this link: https://www.fda.gov/medical-devices/emergency-situations-medical-devices/emergency-use-authorizations
Why is FDA EUA authorization important?
EUA stands for Emergency Use Authorization. A test that has FDA EUA authorization means that the FDA has reviewed available data on the tests’ performance and has authorized it for emergency use. FDA EUA authorization is not the same as FDA approval, which requires a more lengthy and rigorous review process. As of 5/13/2020, no antibody tests are yet FDA approved. While the FDA has allowed many antibody tests to be sold, those without EUA authorization may be less reliable.
Are these tests accurate?
While no test is perfect, there are several considerations to keep in mind when getting a test.
First, we recommend checking with your provider to confirm you are receiving an FDA authorized test whenever possible. All antibody tests with FDA authorization have a sensitivity and specificity in the high 90%. This means they are able to detect the presence of antibodies specific to SARS-CoV-2 with few false positive and false negative results. In contrast, tests without FDA authorization have been reported to have an accuracy as low as 30% in some cases.
Second, some antibody tests are “rapid” tests that can deliver results in under an hour. While these tests may be more convenient, they are generally less accurate than tests that are delivered to a clinically-certified laboratory for processing.
It is important to note that antibody tests are still being studied and no test is yet FDA approved. The test should be used in combination with other information to help identify people with a recent or prior infection with SARS-CoV-2. We recommend that you speak with your provider to help understand your antibody test results. Contact our Personal Health Navigators if you would like to be put in touch with one of our providers to discuss your results.
What test is the Health Center at Hudson Yards using?
At the Health Center at Hudson Yards we are currently referring people for testing at LabCorp. With a physician’s order, patients can get an antibody test at any of LabCorp’s Patient Service Centers, as well as its locations in Walgreens.There is also an option to have the test collected at home.
LabCorp is running an FDA authorized test created by Abbott Laboratories. This test is one of the most reliable tests available. In addition, results from LabCorp will be available in your Mount Sinai electronic medical record.
We can also refer you to Quest who is also using the Abbott test.
In the near future, we will also be able to collect blood for the antibody test at the Health Center. Additionally, in the coming weeks positive test results we receive from LabCorp will be confirmed with Mount Sinai’s own highly specific antibody test which also gives a measurement of the amount of antibody that is present (titer).
Contact our Personal Health Navigators if you are interested in speaking with one of our providers about antibody testing.
Timing and test collection
When is the right time to get an antibody test?
It can take up to two to three weeks after being infected with SARS-CoV-2 for enough antibodies to develop to be able to detect them in the blood. Antibody levels peak at around four weeks. Therefore, it is a good idea to wait at least two to three weeks after the start of the infection to take the antibody test.
Similarly, if you think you were exposed to the virus, but were asymptomatic, you should wait at least two-three weeks from the exposure to have the test
Since the timing of when you take the test is so important, we recommend you talk to your provider about the best time to be tested.
How is the sample for the antibody test collected?
The antibody test is performed by taking a blood sample at the physician’s office or lab patient service center. The sample is then sent to a central laboratory for processing.
How long does it take to get a result?
Turnaround time may vary depending on where you get tested. Results are usually available 1 to 3 business days after testing.
How much does the test cost?
Under the Families First Coronavirus Relief Act (FFCRA), most insurance providers are required by the federal government to cover the test. However, we recommend you check with yours to be sure. Labs and medical practices may charge additional fees for things like blood collection and test interpretation so it’s important to ask about these before you go for the test.
Interpretation of Results
What does a positive or negative result mean?
A positive antibody test result suggests that an individual most likely has been infected with the SARS-CoV-2 virus and has developed detectable antibodies to SARS-CoV-2. It is possible that a positive result is due to antibodies to a different, similar virus. This is called a false positive. The chances of a false positive depend on a number of factors including the accuracy of the test itself as well as how common the infection is in the population.
A negative test result suggests that, at the time of the test, an individual had not developed detectable antibodies to SARS-CoV-2. A negative result could be because the individual has not been infected with the virus, that they were tested before they developed detectable antibodies, or that they did not have an adequate immune response to the virus.
What does an equivocal or indeterminate result mean?
An equivocal result means that the test could not determine whether or not the individual’s blood sample had antibodies to SARS-CoV-2. It is neither positive nor negative. People with an equivocal result should be re-tested to determine if they have antibodies. An equivocal result could happen if there were not enough antibodies present to detect at the time of the test or if there was a technical problem with the test.
Does a positive antibody test mean that I am immune to coronavirus?
There is currently no conclusive evidence that having antibodies to SARS-CoV-2 means individuals are immune. Based on what is known about other infections, experts believe it is likely that antibodies offer some protection. It is also not known how much antibody is needed for protection and how long immunity may last. Ongoing research on SARS-CoV-2, including at Mount Sinai, is looking to answer these questions. Research on similar coronaviruses like SARS and MERS suggests that antibodies may protect from reinfection for several years.
Since we don’t know for certain that people with antibodies are immune, it is important to still practice precautions like social distancing, even if you have antibodies.
If I test positive for antibodies, am I contagious?
Having antibodies does not indicate whether or not you are contagious. People with antibodies can still have detectable virus in their bodies, especially if they were recently infected. If several weeks have passed since your infection, you are less likely to be contagious. Nevertheless, it is important to still practice precautions like social distancing, even if you have antibodies.
If I test positive for antibodies, can I donate my plasma to help people who have COVID-19?
People who have fully recovered from COVID-19 for at least two weeks are encouraged to consider donating plasma, which may help save the lives of other patients. COVID-19 convalescent plasma must only be collected from recovered individuals if they are eligible to donate blood. Learn more about Mount Sinai’s Convalescent Plasma program.
Additionally, some providers may require individuals had a prior diagnosis of COVID-19 as documented by a laboratory test. Please check with the provider offering the convalescent plasma therapy program for specific donor eligibility criteria.
Definitions and Explanations of Testing Terms
What are IgG and IgM antibodies?
The body mounts an immune response upon encountering a virus. Immune molecules called antibodies are a crucial part of this response. Antibodies help immune system cells identify and destroy other cells that are infected with the virus.
In general, for many types of infections, IgM is the first type of antibody to appear. IgG often appears a bit later, lasts longer in the body, and is often the antibody responsible for longer term immunity. The timing and levels of IgM and IgG antibodies in SARS-CoV-2 infection are still being worked out. It appears that IgM and IgG levels begin to rise within the first few days of infection in many people. Experts believe that IgG levels peak around 28 days after the onset of infection. It is still not known how long antibodies to SARS-CoV-2 remain present, if they confer immunity, and for how long.
What does the sensitivity of a test mean?
Sensitivity is the ability of a test to correctly identify those with the disease. A test with high sensitivity will result in a low false negative rate. This is especially important for diagnostic tests, as a false negative result means that an individual with COVID-19 would mistakenly believe they were not infected.
What does the specificity of a test mean?
Specificity is the ability of the test to correctly identify those without the disease. A test with high specificity will result in a low false positive rate. This is especially important for antibody tests, as a false positive result means that an individual without antibodies would mistakenly believe they were protected from the virus.
Juanjuan Zhao, et al, Antibody responses to SARS-CoV-2 in patients of novel coronavirus disease 2019, Clinical Infectious Diseases, , ciaa344, https://doi.org/10.1093/cid/ciaa344
Long, Q., Liu, B., Deng, H. et al. Antibody responses to SARS-CoV-2 in patients with COVID-19. Nat Med (2020). https://doi.org/10.1038/s41591-020-0897-1
FDA Fact Sheet, Serological Testing For Antibodies To Sars-Cov-2 Infection