What it measures
A protein from the outer coat of the hepatitis B virus (HBsAg). It is in the blood during a current infection, whether recent or long-term. It is the main test for current hepatitis B.
Why people test it
- Checking for current hepatitis B, with or without symptoms.
- Routine screening in pregnancy, before blood or organ donation, or for some jobs.
- Checking after possible exposure, such as condomless sex, shared needles or a needlestick injury.
- Monitoring people with long-term hepatitis B.
Typical range
There is no numeric range. The result is reported as positive or negative (sometimes reactive or non-reactive), and a positive result is confirmed with further tests. The report shows how that lab reports it.
Finger-prick or vein?
A finger-prick sample is usually fine for this test, and several providers offer a home kit. Others take blood from a vein, at a clinic or with a visiting nurse.