What Does Hepatitis B Surface Antigen Testing Mean?

The hepatitis B surface antigen (HBsAg) is a protein found on the surface of the hepatitis B virus (HBV), often referred to as the "Australian antigen." A positive result in an HBsAg test typically indicates the presence of the hepatitis B virus in the body. However, a positive HBsAg alone is not sufficient to determine the stage or severity of the infection. Doctors usually recommend a complete hepatitis B panel, also known as the "hepatitis B five-panel test," to better understand the patient's condition.

In this five-panel test, if the first, third, and fifth markers are positive, it is referred to as "big three positive" (HBeAg positive), indicating active viral replication. On the other hand, if the first, fourth, and fifth markers are positive, it is known as "small three positive" (HBeAg negative), which may suggest a lower level of viral activity. Following this, HBV-DNA testing is crucial to determine whether antiviral treatment is necessary.

It's important to note that relying solely on HBsAg testing can be misleading. In some cases, even if HBsAg results are negative, HBV-DNA may still be detectable in the blood. This can indicate a hidden or occult hepatitis B infection. Such cases may also show signs of active hepatitis, emphasizing the need for more comprehensive diagnostic approaches. Therefore, a combination of tests is essential for accurate diagnosis and effective management of hepatitis B.