HBsAg (ELISA)

Function

The Hepatitis B Surface Antigen (HBsAg) test is the primary diagnostic tool used to identify an active infection with the Hepatitis B Virus (HBV). HBsAg is a protein located on the surface of the virus. When this antigen is detected in the blood, it indicates that the virus is present and the individual is potentially infectious to others. Using the ELISA (Enzyme-Linked Immunosorbent Assay) method provides a highly sensitive and specific way to detect even minute amounts of this protein during the early stages of infection.

Why it is Ordered

Physicians order the HBsAg test for several critical reasons:

• Screening: To check for infection in high-risk groups, pregnant women (to prevent mother-to-child transmission), or blood donors.
• Diagnosis: To evaluate patients presenting with symptoms of acute hepatitis, such as jaundice, dark urine, or extreme fatigue.
• Monitoring: To determine if a known HBV infection has become chronic. If HBsAg persists for more than six months, the patient is diagnosed with chronic Hepatitis B.
• Pre-treatment Screening: Before initiating immunosuppressive therapy or chemotherapy, which could reactivate a latent HBV infection.

Associated Conditions

The presence of HBsAg is directly associated with:

• Acute Hepatitis B: The initial stage of infection where the antigen appears before symptoms develop.
• Chronic Hepatitis B: A long-term infection that can lead to severe liver damage, including cirrhosis and hepatocellular carcinoma (liver cancer).
• Carrier State: Individuals who do not show symptoms but can still transmit the virus.