Antibody FAQs
 
 
 

Why should I get an Antibody test?

An antibody test will tell you if you were exposed to COVID-19 and have developed antibodies to the virus. It is helpful to those:

  • who were not able to get tested while they were sick and would like confirmation that they had COVID-19

  • who think they might have had COVID-19 but have now recovered

  • who want to know if they had an asymptomatic case of COVID-19

  • who were exposed to others who had COVID-19, but experienced no or light symptoms and want to know if they developed antibodies to the disease

  • who want to know if they developed antibodies to the disease

What is an Antibody test?

Antibody tests, or serology tests, look for antibodies in the blood. These antibodies form as a person is recovering from COVID-19 and fight the disease.

What do Antibody tests measure?

Antibody tests analyze blood, serum or plasma samples for the presence of immunoglobulin M [IgM] and immunoglobulin G [IgG]. COVID specific IgM and IgG are antibodies associated with the coronavirus (SARS-CoV-2). IgM forms in the body as it first begins to recover and provides the first line of defense during viral infections. The presence of IgM antibodies indicates that you have been infected with COVID-19 fairly recently. Some tests also measure IgA, an antibody found mainly in the respiratory and digestive tracts - that is also formed at the beginning of the infection.

Most antibody tests will look for IgG. Presence of COVID specific IgG antibodies means that you have been infected with COVID-19 and are in a later stage of recovery. These antibodies form after the IgM and IgA antibodies. COVID-19 patients, who get tested soon after developing symptoms, may not yet have begun to produce a detectable amount of IgG antibodies. Ideally, for optimal IgG antibody test accuracy, patients should get tested 2-6 weeks after they are symptom free.

If I have a positive antibody test, am I no longer contagious?

Not necessarily. Antibodies form in the body to help you fight disease. The detection of COVID-19 IgM antibodies tends to indicate a recent exposure to COVID-19, and detection of COVID-19 IgG antibodies indicates a later stage of infection - and that the patient has started to recover.  The CDC’s present guidance states that people with COVID-19 should be isolated for at least 10 days after symptom onset and until 24 hours after their fever subsides without the use of fever-reducing medications.

If I test positive for antibodies, am I immune to later infection?

Not necessarily. It is not known at this time if, or for how long, IgG antibodies confer immunity to COVID-19, but researchers believe that they most likely convey some level of protection against future infection. That protection may be short lived, and may vary from person to person.

How accurate are Antibody tests?

In general, even the best tests are not 100% accurate. False positive and negative results are possible. As of February 10, 2022, 85 tests have received Emergency Use Authorization [EUA] from the FDA. EUAs are issued for each individual test with certain conditions of authorization required of the manufacturer and authorized laboratories.

What is the difference between a test’s “Sensitivity” and “Specificity?”

As you read about different antibody tests, you will need to understand the following terms.

  • "Sensitivity" is the ability of a test to correctly identify those patients with the disease (true positive rate).

  • "Specificity" refers to the ability of the test to correctly identify those people without the disease (true negative rate).

  • The Positive [PPV] and Negative Predictive Values [NPV] are the proportions of positive and negative results that are true positive and true negative results, respectively.

Can you test positive for both the virus and the antibodies?

Yes, it is possible to test positive for both antibodies and the virus itself. This means that your body is producing the antibodies to fight the virus, but at the same time you still are recovering. This is possible, even if you aren’t showing any of the classic COVID-19 symptoms.

Can you test positive for the virus, but negative for antibodies?

Yes. There may be several reasons for this. If you get tested for antibodies too soon after infection, you may not have formed a detectable level of antibodies. That is why it is advisable to wait 2-6 weeks after symptoms are gone. It may also be possible for some people to clear the viral infection from their system without ever forming detectable antibodies. This may be a disappointing answer, but it happens.

If I was exposed to COVID-19, but never had symptoms, will I have antibodies?

Yes, it is possible.

When should I get an Antibody test?

Ideally, for optimal accuracy, patients should get tested 2-6 weeks after they are symptom-free. If you test prior to that, the level of antibodies in your blood may not be high enough to register a positive result.

It is not known at this time if, or for how long, antibodies confer immunity to COVID-19, but antibodies are believed to stay in your system for an extended period of time. For other coronaviruses like SARS and MERS, antibodies seemed to peak within months of an infection - and last for a year or more.

How do I read Antibody test results?

Most tests will give you a positive or negative result. Some will test for IgM and IgG separately, and some will break the score down, or only test for one type of antibody. A few will give you an antibody level. Some research studies require a certain ‘titer’ score. At this time, your test results will not tell you a titer score.

If I test positive for antibodies, can I help other people who are infected with COVID to recover?

Yes. If you have recovered from COVID-19, you can donate your plasma to help others. Every plasma donation can save up to 3 lives! The plasma in Survivors contains antibodies that can be used in two types of treatments to help others recover from COVID-19: direct transfusion and hyperimmune globulin (HIg).

  • Plasma that has been collected from recovered patients can be given to (or transfused directly into) people experiencing serious complications from COVID-19.

  • Plasma that has been collected from recovered patients and is further processed into hyperimmune globulin, is a potential treatment for people at risk for serious complications from COVID-19.

Please consider making a plasma donation to help those in need. You may give multiple times! Click here for locations where you can donate plasma.

We are in a time of national blood shortage, and all blood donations are needed. Some blood centers, such as the Red Cross, New York Blood Centers and others, are testing blood donations for antibodies. If your blood contains antibodies, they will extract the plasma from your donation and use it to help a COVID-19 patient, as well as use the other parts of your blood for important life saving transfusions. Click here to find out where you can sign up to give blood. Please donate today!