The Hepatitis B Surface Antibody (HBsAb) Test

The hepatitis B surface antibody test (HBsAb) detects proteins called antibodies that are produced by the immune system in response to the hepatitis B virus (HBV). The test is used to determine if you are immune to the virus after natural exposure or vaccination. The HBsAb test requires a blood sample, which is analyzed in a lab.

A positive or "reactive" result means you're immune to the hepatitis B virus. A negative or "non-reactive" result means you're not immune to the virus.

This article explains what the hepatitis B surface antibody test is for, when it is used, and how the test is performed. It also offers insights into what a positive and negative test result means.

Purpose of the Hepatitis B Surface Antibody Test

The HBsAb test determines the presence and quantity of HBV antibodies in your blood in order to establish how immune you are to the virus. These antibodies are "encoded" by your immune system when it encounters the HBV virus through blood or sexual contact, or if you are vaccinated with the hepatitis B vaccine. Your body uses the antibodies to attack the virus if it appears again.

The HBsAb test may be used to look for prior exposure to HBV (and to tell how recent it was). By comparing levels of IgM and IgG, a healthcare practitioner can also use the test to monitor your recovery from an acute HBV infection.

Additionally, the HBsAb test can reveal whether you are successfully vaccinated, not successfully vaccinated, or indeterminately vaccinated. A booster vaccine may be needed if the HBsAb level drops below protective levels.

The HBsAb test should not be confused with either the hepatitis B surface antigen (HBsAg) test or the hepatitis B core antibody (HBcAb) test, both of which are used to determine if you have been infected with HBV.

How the HBsAb Test Is Done

The HBsAb test is done by drawing a blood sample that gets sent to a lab for analysis. Your healthcare provider will evaluate the results in line with your vaccination history, symptoms, and exposure risk, as well as the results of other hepatitis tests.

Interpreting Results

Your HBsAb test result may either be positive or negative, but the interpretation can vary based on the results of your HBsAg and HBcAb tests.

Positive

When the HBsAb result is positive or "reactive"—meaning the surface antibodies are present—it usually means that you have recovered from a recent or prior hepatitis B infection and are immune to the virus. If both the HBsAb and HBcAb are positive, a person is said to be immune due to natural infection.

If you received the hepatitis B vaccine, a positive HBsAb result on its own is also an indication of immunity.

Negative

An HBsAb test that is negative or "non-reactive" can mean many different things. In general, it means that you are not immune to the virus.

Even so, there are different ways to interpret the results based on their relationship to the other HBV tests.

Follow-Up

If your HBsAb is positive, you cannot infect others and do not require vaccination.

If all three tests are negative—meaning that you have never been exposed to the virus—you will be advised to get the HBV vaccine.

If your HBsAb test is negative but the other tests are positive, your healthcare provider will need to evaluate you further. Whether your infection is acute or chronic, you still have the ability to infect others and will be counseled on ways to avoid that.

If the results are unclear, all three tests will be repeated.

Summary

The hepatitis B surface antibody (HBsAb) test detects and measures antibodies produced by the immune system in response to the hepatitis B virus. It is one of several tests used to diagnose hepatitis and is used specifically to determine your level of immunity to the virus.

The test involves a simple blood draw that will return either a positive or negative result. A positive result generally means that you are immune to the virus and cannot infect others. A negative result can mean any number of things based on the results of the other tests.

A Word From Verywell

If all of your hepatitis tests are negative, it indicates that you have not been exposed to the virus and are not immune. If this is the case, talk to your healthcare provider about getting vaccinated whether or not you are at risk of hepatitis B.

Even if you are immune to hepatitis B, you may still be at risk for other types of hepatitis, including hepatitis C.