Hepatitis Bs (Surface) Antigen (HBsAg)

Description

What is HBsAg?

Hepatitis B Surface Antigen (HBsAg) test is used to determine the presence of Hepatitis B viral infection by measuring the amount of HBsAg in the blood. Hep B virus spreads mainly through body fluids or unsafe sexual intercourse. Hep B antigen is expressed on the surface of Hepatitis B virus and its detection is a preliminary test to check the infection at an earliest possible stage. A positive Hep B surface antigen test requires further testing to determine the level of infection in the body.
In some cases uncontrolled levels of Hep B infection can lead to chronic hepatitis infection and liver cirrhosis.
Immunocompromised patients and infants are more prone to develop severe symptoms of chronic hepatitis.

Why is HBsAg done?

• To detect Hepatitis B virus infection in patients having symptoms suggestive of Hepatitis
• To screen for Hepatitis B infection following accidental exposure to HBV e.g. in healthcare workers. Repeat testing is recommended after 6 weeks post exposure
• To screen for Hepatitis B infection in individuals who are at risk of acquiring infection like IV drug users, sex workers, hemodialysis patients, prisoners, etc.
• To screen for Hepatitis B infection during pregnancy to prevent transmission of infection from mother to child

What does HBsAg Measure?

HBsAg test detects the presence or absence of Hepatitis B Surface Antigen (HBsAg) in the blood.

Hepatitis B virus is one of the five main hepatitis viruses, referred to as types A, B, C, D and E and is the causative agent of Hepatitis B (infection in the liver). Hepatitis B Surface Antigen (HBsAg) is present on the surface of the Hepatitis B virus (HBV). HBsAg is present in the blood of patients with viral hepatitis B (with or without clinical symptoms).

HBsAg is the first marker appearing in the blood at 6 to 16 weeks following exposure to HBV. In most cases after an acute infection, this virus clears up on its own in 1 to 2 months after the onset of symptoms. But in some people, the virus does not go away and results in chronic infection which over the years may lead to liver damage (scarring or cirrhosis) or liver cancer. Persistence of HBsAg for more than 6 months indicates the development of either a chronic carrier state or chronic HBV infection.

Interpreting HBsAg results

Interpretations

A “Reactive” or “Positive” HBsAg test result means that the person is infected with Hepatitis B virus. If a person tests “positive,” then further testing is required to determine if this is a new “acute” infection or a “chronic” Hepatitis B infection or chronic HBV carrier state.

A “Non-reactive” or “Negative” HBsAg test result means that the person is not infected with Hepatitis B virus.