Hepatitis B Surface Antigen (HBsAg)

The Hepatitis B Surface Antigen (HBsAg) test detects the presence of the surface antigen of the hepatitis B virus in the blood. This is one of the earliest markers of acute or chronic hepatitis B infection and is used to screen, diagnose, and monitor HBV infection.

1. What Is HBsAg?

• HBsAg is a protein on the surface of the hepatitis B virus (HBV).

• Its presence in the blood indicates that the person is infected with HBV and can potentially transmit the virus to others.

• HBsAg is the first marker to appear in acute infection and may persist in chronic infection.

2. Why Is the HBsAg Test Performed?

This test is used to:

• Diagnose an active hepatitis B infection (acute or chronic).

• Screen for HBV infection before surgery, blood donation, or organ transplant.

• Monitor chronic hepatitis B patients and evaluate treatment effectiveness.

• Assess risk of transmission to others (e.g., pregnant individuals, healthcare workers).

3. Interpreting HBsAg Results

🔹 Positive (Reactive) HBsAg:

• Indicates an active hepatitis B infection.

• If present for more than 6 months, the infection is considered chronic.

🔹 Negative (Non-reactive) HBsAg:

• No active hepatitis B infection at the time of testing.

• May still require other HBV tests to determine prior exposure or immunity (e.g., anti-HBs, anti-HBc).

4. What Can Affect HBsAg Test Accuracy?

• Early stage of infection (HBsAg may not be detectable yet).

• False positives in low-risk individuals—confirmation by repeat or additional testing may be needed.

• Immunosuppressive states may alter viral markers.

5. How Is the Test Performed?

• A blood sample is drawn from a vein in the arm.

• No fasting or special preparation is required.

6. When to See a Doctor

🚨 Contact your healthcare provider if you:

• Have symptoms of hepatitis (e.g., fatigue, jaundice, dark urine).

• Were exposed to someone with hepatitis B or are at risk (e.g., healthcare workers, travelers).

• Receive a positive result and need further evaluation or treatment.

🔹 Key Takeaways

✅ HBsAg is the primary marker for identifying active hepatitis B infection.

✅ A positive result indicates potential infectivity and may signify chronic infection.

✅ Early detection is important for management, treatment, and preventing transmission.