HBsAg (Hepatitis B Surface Antigen)
Hepatitis B surface antigen (HBsAg) is a protein on the outer surface of the hepatitis B virus. It appears in blood 1–10 weeks after exposure, before symptoms begin, and either clears within 6 months (acute infection that resolves) or persists (chronic hepatitis B). HBsAg is the primary screening test for hepatitis B and is part of most routine pre-surgical, antenatal, and pre-employment health checks in India.
Expected Result
Normal
Negative (Non-reactive)
Positive results are confirmed with a second test. Full HBV panel (HBsAg, anti-HBs, anti-HBc, HBV DNA) characterizes the stage of infection.
This is a qualitative test — results are reported as positive or negative rather than as a numeric range. Interpretation may vary by laboratory method; always review with your doctor.
What a Negative Result Means
A negative HBsAg means you do not have current active hepatitis B. It does not, however, distinguish 'never infected' from 'previously infected and cleared' — adding anti-HBs and anti-HBc makes this distinction. A negative HBsAg in someone at ongoing risk (healthcare worker, unvaccinated) should prompt vaccination if anti-HBs is also negative.
What a Positive Result Means
A positive HBsAg confirms hepatitis B infection. The next step is to determine whether it is acute or chronic: a positive test that turns negative within 6 months indicates acute infection that has cleared; persistence beyond 6 months is chronic hepatitis B. Follow-up tests — HBeAg, anti-HBe, HBV DNA, liver function, and fibroscan — stage the infection and guide antiviral treatment decisions.
Frequently Asked Questions
If HBsAg is positive, am I contagious?
Yes. HBsAg-positive individuals can transmit hepatitis B through blood, unprotected sex, and from mother to child during childbirth. Close contacts should be tested and vaccinated if not immune. HBV DNA level determines infectivity — high viral loads mean higher transmission risk. Universal precautions and vaccination prevent most transmissions.
Can a positive HBsAg be a false positive?
Rare but possible. Very weak positives may be false positives, especially in low-prevalence populations. Any positive HBsAg should be repeated, and the full hepatitis B panel (anti-HBs, anti-HBc total, IgM anti-HBc, HBeAg, HBV DNA) should be done to confirm and characterize the infection.
Will my HBsAg ever turn negative?
In acute hepatitis B, HBsAg typically clears within 3–6 months — adults have a ~95% chance of clearing. In chronic hepatitis B, spontaneous clearance is only 0.5–1% per year. Antiviral treatment (tenofovir, entecavir) effectively suppresses the virus but rarely eliminates HBsAg. A sustained HBsAg-negative result with anti-HBs appearance is called 'functional cure.'
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This information is for educational purposes only and should not replace professional medical advice. Always consult your doctor for interpretation of your test results.
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