HBsAg (Hepatitis B Surface Antigen) Test

The HBsAg test detects the presence of the hepatitis B surface antigen, a protein on the surface of the hepatitis B virus (HBV), in the blood. This antigen is the first measurable sign of an active hepatitis B infection and indicates that the virus is present and the person is infectious.

Purpose

• Screening: The HBsAg test is commonly used to screen for hepatitis B infection, especially in individuals at high risk, such as healthcare workers, pregnant women, or those with a history of unprotected sex or intravenous drug use.
• Diagnosis: It helps diagnose both acute and chronic hepatitis B infections.
• Monitoring: Used to monitor the effectiveness of treatment for chronic hepatitis B and to assess the infectiousness of a patient.

How It Works

• Antigen Detection: The test detects the hepatitis B surface antigen in the blood. The presence of HBsAg indicates that the hepatitis B virus is actively replicating in the liver.

Interpreting Results

• Positive Result: Indicates an active hepatitis B infection, either acute or chronic. If HBsAg is detected for more than six months, it typically suggests a chronic infection.
• Negative Result: Suggests that there is no current infection with hepatitis B, although it does not rule out past infections that have been resolved or the presence of other hepatitis B markers.

Clinical Relevance

• Acute Infection: HBsAg is usually detectable 1 to 10 weeks after exposure and can persist for months in acute cases.
• Chronic Infection: If HBsAg persists beyond six months, the infection is considered chronic, which carries a risk of liver complications, including cirrhosis and liver cancer.
• Screening and Prevention: Regular screening can help identify infected individuals, allowing for early intervention and reducing the risk of transmission. It is also essential in screening blood donors to ensure safe blood supplies.

HBsAg is a critical marker for hepatitis B management, helping guide treatment decisions, monitoring the course of the disease, and implementing preventive measures to protect others from infection.