Hepatitis B Surface Antigen Test (HBsAg) with Reflex Confirmation

This test detects hepatitis B surface antigen (HBsAg), a protein found on the outer coat of the hepatitis B virus, using an immunoassay. HBsAg in the blood means the virus is currently present. If the screening result is reactive, the lab automatically performs a confirmatory neutralization test on the same sample, in which an antibody specific to HBsAg is added to check that the signal is genuinely hepatitis B surface antigen.

Adults who want to know whether they currently have hepatitis B, people with a recent possible exposure (sexual contact, shared needles, or living with someone who has hepatitis B), people born in regions where hepatitis B is common, people with HIV or hepatitis C, and anyone whose clinician has seen unexplained raised liver enzymes. If you have never been screened, the CDC recommends the three-marker panel rather than HBsAg alone, because it also shows past infection and immunity.

Any time; no fasting needed. After a specific exposure, HBsAg can become detectable as early as 1-2 weeks but sometimes not until 11-12 weeks, so a negative result in the first three months may need repeating. People with ongoing risk who are not immune should test periodically, at a frequency agreed with a clinician. HBsAg is also part of routine testing in every pregnancy.

A non-reactive (negative) result means hepatitis B surface antigen was not detected, so there is no sign of current infection at the time of the test. A reactive result is automatically checked with a confirmation test. A confirmed positive HBsAg means hepatitis B virus is present, either a recent infection or a chronic one, and should be reviewed with a clinician promptly. Next steps usually include HBV DNA (viral load), liver tests, an evaluation by a clinician experienced in hepatitis B, and offering testing and vaccination to household and sexual contacts. Your results are informational; please review them with a clinician.