What Is the Hepatitis B Surface Antibody (HBsAb) Test?

Are you immune to the hepatitis B virus?

Nurse and patient examining medical records
What does it mean if your hepatitis surface antibody (HBsAb) test is positive or negative?. Slobodan Vasic/E+/Getty Images

The HBsAb test, or hepatitis B surface antibody test, looks for antibodies that your immune system makes in response to the surface protein of the hepatitis B virus. The hepatitis B surface antibody is also referred to as anti-HBs and should not be confused with HBsAg, which stands for hepatitis B surface antigen. 

What Is the Hepatitis B Surface Antibody?

When you are exposed to Hepatitis B, your body mounts an immune reaction against it as an invader.

This happens whether you are exposed due to blood or sexual contact or if you are vaccinated with the Hepatitis B vaccine. The hepatitis B virus has proteins on its surface (antigens) that cause your immune system to produce antibodies. With the vaccine, the sample contains the protein only and not the virus itself.

The first response your body will make when exposed to hepatitis B is to manufacture Hepatitis B IgM antibodies. These early antibodies are produced to fight against several parts of the virus including its core. These antibodies are seen in the initial response, but they eventually fade away.

Your immune system then begins to produce IgG antibodies. It continues to produce these antibodies for the rest of your life. In this way, your immune system is always ready to attack Hepatitis B virus when it is exposed to it.

What Does a Positive or Negative HBsAb Test Mean?

Positive - When HBsAb is positive (antibodies are present,) it usually means that you have recovered from a hepatitis B infection and have some immunity, or that you once received the hepatitis B vaccination and are immune.

Negative - If your HBsAb test is negative, it can mean many different things—but, in general, it means you are not immune to the Hepatitis B virus. If your other Hepatitis B tests (both HBsAb and other hepatitis tests) are negative, it means you are either not infected or that you are in the very early incubation stage of infection, prior to the point at which antibodies would be formed.

If you test is negative, your doctor may recommend getting the vaccine.

Negative but other hepatitis tests are positive - Your HBsAb test, however, may be negative even when other Hepatitis B tests are positive, showing active or chronic infection. This is why further testing is necessary, especially for the hepatitis B surface antigen (HBsAg), which shows that the virus itself is circulating in your bloodstream and that you have an active or chronic infection.

Learn more about how to interpret the different hepatitis tests.

When Is the HBsAb Test Done?

This HBsAb test may be done to look for prior exposure to Hepatitis B or whether your vaccination was successful.

It may also be done if you have Hepatitis B to see if you are recovering. While it is standard (and has been since 1991) to vaccinate babies and children for Hepatitis B, many adults were not vaccinated as children and may be at risk.

It is also possible for your antibody levels to drop over the years and if the test is negative, you may need a booster.

How Is the HBsAb Test Done?

The HBsAb test is done by drawing a blood sample which is sent to the lab for analysis. Your doctor will receive the results and evaluate them in light of your vaccination history, exposure risk, symptoms, and the results of other hepatitis tests.

A Word From Verywell

Ask your doctor if you have further questions about the test and why it is being performed. As noted above, if your HBsAb is positive, it either means you have had the infection in the past or received the vaccine and are now immune.

If your test is negative, you and your doctor will then need to evaluate your other hepatitis tests to figure out what is going on. If all of your hepatitis tests are negative, it indicates that you have not been exposed to the virus (or received the shot) and are not immune. If this is the case, talk to your doctor about getting immunized, whether or not you have risk factors for acquiring hepatitis B.

It's important to note that many people who become infected with the hepatitis B virus have no obvious risk factors for getting the infection. It takes only a small amount of blood to transmit the virus (think: open sore on your hand touching an object that a person who has the disease may have touched). Even sharing a toothbrush or kissing is enough to transmit the infection. Vaccination, in this case, can protect you against unknown sources of the infection.

If your HBsAb test is negative but other hepatitis tests are positive, your doctor will need to evaluate you further. It could be that you have an active infection, which should be monitored closely, or that you have now developed a chronic hepatitis B infection. Chronic infections can lead to complications down the line, some as severe as cirrhosis and liver cancer, so it is very important to follow up with your doctor and develop a plan of action, whether that means treatment or careful monitoring.

As a final note, even those who are immune to hepatitis B via immunization are still at risk for other types of hepatitis. Take a moment to review these safety tips on how to prevent hepatitis infections.

Sources:

Kasper, Dennis L.., Anthony S. Fauci, and Stephen L.. Hauser. Harrison's Principles of Internal Medicine. New York: Mc Graw Hill education, 2015. Print.

Kumar, Vinay, Abul K. Abbas, and Jon C. Aster. Robbins and Cotran Pathologic Basis of Disease. Philadelphia: Elsevier-Saunders, 2015. Print.

Song, J., and D. Kim. Diagnosis of Hepatitis B. Annals of Translational Medicine. 2016. 4(18):338.

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