Hepatitis B surface antigen (HBsAg)

What it measures

Detects the outer envelope protein of hepatitis B virus. It is the main screening test for current HBV infection and is used for blood donors, antenatal screening and pre-operative workup.

Specimen and preparation

• Specimen: Serum or plasma
• Tube: Gold top
• Preparation: No fasting needed.

Reference range

Reference ranges differ between laboratories, methods and populations. Always use the range printed on your own lab report.

Causes of high values

• Acute hepatitis B (appears 1–10 weeks after exposure)
• Chronic HBV infection if positive for more than 6 months
• Inactive HBV carrier state

Method

CLIA/ECLIA or ELISA; rapid immunochromatographic cards for screening

Good to know

Reactive screening results should be confirmed (neutralization or repeat assay). Loss of HBsAg with appearance of anti-HBs marks recovery.

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