What to Know About Antibody Testing

What is a COVID-19 antibody test?

A COVID-19 antibody test is a blood test that can tell if you previously had COVID-19 and have since recovered. The test involves having your blood drawn at a healthcare facility. It checks for the presence of a particular antibody your body makes when it’s fighting the virus. These antibodies appear in your bloodstream after you’ve been infected. This test is not the same as a nasal swab test and does not check for the presence of the virus that causes COVID-19. You should not get this test if you’re currently experiencing symptoms of COVID-19.

What’s the purpose of antibody testing?

We still have much to discover and learn about the virus and its resulting disease. For the individual patient, this test is currently unlikely to change your medical management or what precautions you need to use such as physical distancing or masking in public. At this time, the test is most useful to understand how much the disease has spread in the community and potentially predict if a second surge of cases is likely to occur. The results may also help us develop new treatments and even a vaccine.

How accurate is the antibody test?

Accuracy of a lab test is measured in “sensitivity” and “specificity.” Sensitivity is the test's ability to correctly identify those with antibodies (true positives) and specificity is the test's ability to identify those without the antibodies (true negatives). The test used by the UW virology lab is very sensitive with almost 100% of people who have been infected having a positive test by 25 days after infection. It is also very specific being negative in more than 99% of people who did not have COVID-19. One challenge with this test is that due to the overall low number of people with COVID-19 in the community, it is possible to have a “false positive” result. This means the test will be positive when the person never was infected. This is true for all antibody tests, including a very good one like the one used at UW Medicine.

Who qualifies or doesn’t qualify for an antibody test?

You should not get an antibody test if you’re currently experiencing symptoms of COVID-19, such as a fever, cough, shortness of breath, chills, repeated shaking with chills, muscle pain, headache, sore throat, or new loss of smell or taste. However, you may qualify for an antibody test if you had a confirmed case of the disease and have since recovered, were previously experiencing symptoms but never got tested, or were exposed to COVID-19 more than 14 days ago. Check your individual insurance plan to see if you’re covered for this type of test.

How long do the test results take?

Results are usually available within one day.

What does a negative result mean?

If your results are negative, it means you don’t have the COVID-19 antibody in your bloodstream and likely never had the disease.

What does a positive result mean?

If your results are positive, it means you previously had a COVID-19 infection. We do not yet know if a positive test result means that a person is immune, and if it does, for how long immunity might last. We hope to learn more in the coming months. If your test is positive, you should continue to follow public health recommendations on social/physical distancing, hand hygiene, environmental cleaning, staying home when ill and mask use. Talk to your doctor about what your results mean.

How can I get an antibody test?

Currently, antibody tests are only available when ordered by a healthcare professional. Antibody tests involve traveling to a healthcare facility to get your blood drawn, so an appointment is also required. To ask your doctor about getting an antibody test, schedule an appointment by calling 206.520.5000 or by logging in to our MyChart patient portal.