HbsAg (Hepatitis B)

What is HBsAg?

HBsAg (Hepatitis B surface antigen) is a protein found on the outer shell of the Hepatitis B virus. Detecting it in blood tells whether a person is infected with Hepatitis B.

Key Parameter

Why it is done

• Routine screening for people at risk (e.g., healthcare workers, travelers, pregnant women)
• Evaluation of symptoms such as jaundice, fatigue, or abnormal liver tests
• Monitoring of patients on antiviral therapy or with chronic Hepatitis B

Early Detection

It can help identify signs of Hepatitis B infection, but it does not diagnose the disease on its own. A doctor interprets the result together with symptoms, history, and other tests.

What an abnormal result means

A positive HBsAg indicates an active infection. A negative result does not guarantee immunity; vaccination status should be checked. Results can be influenced by factors such as recent vaccination, certain medications, or laboratory variability.

Who should get it

• Individuals with risk factors (unprotected sex, IV drug use, blood transfusion, close contact with an infected person)
• Pregnant women to prevent mother‑to‑child transmission
• Travelers to endemic areas
• Patients with unexplained liver enzyme elevations

Summary

HBsAg testing detects active Hepatitis B infection and helps guide treatment and prevention strategies.

Preparation

• No fasting required.
• If you are also having a fasting test (e.g., blood sugar), follow the fasting instructions for that test.
• Bring a list of current medications.
• Avoid alcohol and strenuous exercise 24 hours before the test.

Procedure

A healthcare professional will draw a small amount of blood (about 5–10 mL) from a vein in your arm using a sterile needle. The process takes less than 5 minutes. You may feel a brief pinch.

Aftercare

• Apply gentle pressure to the puncture site until bleeding stops.
• You can resume normal activities immediately.

Note

Confirm any specific preparation with your doctor or the lab. This information is general educational guidance and not a substitute for professional medical advice.