Infectious Disease
Hepatitis B surface antigen
Hepatitis B surface antigen (HBsAg) is a protein on the outer coat of the hepatitis B virus and is the primary marker used to screen for current HBV infection. At the point of care it is most often run as a qualitative lateral-flow rapid test that reports a Reactive or Non-reactive result rather than a numerical value.
Why it is measured
HBsAg appears early in infection and persists in chronic carriers, so as a marker it underpins antenatal screening, blood and organ donor checks and decentralised hepatitis programmes. A rapid same-visit result helps connect reactive individuals to confirmatory testing and care without a return trip.
| Typical range | Qualitative result for adults: the expected (normal) finding is Non-reactive, also reported as negative. The assay reports Reactive or Non-reactive rather than a concentration, so there is no numerical reference interval. For context, lateral-flow rapid tests typically detect HBsAg down to roughly 0.1 to 4 IU/mL depending on the kit, with the most sensitive cards quoting an analytical sensitivity near 0.1 IU/mL and many field tests being less sensitive. Cut-off, sensitivity and the meaning of a faint test line vary by method and manufacturer, so always read against the specific instructions for use. |
|---|---|
| Sample | Finger-prick capillary whole blood, venous whole blood, serum or plasma, depending on the kit. Oral fluid is not used for HBsAg detection. |
| Turnaround | About 15 to 30 minutes for most lateral-flow rapid tests, read within the manufacturer's stated window. |
Point of care devices that report it
- Abbott Determine HBsAg 2
- Abbott (SD) Bioline HBsAg WB
- bioMerieux VIKIA HBsAg
- SD Biosensor STANDARD Q HBsAg
Questions, answered
Does a reactive point-of-care HBsAg result confirm hepatitis B?
No. A reactive rapid result is a screening flag, not a diagnosis. Guidelines require a confirmatory laboratory HBsAg assay and a fuller hepatitis B panel (such as anti-HBc, HBsAg neutralisation or a different platform) before infection is confirmed. This record is educational and not a substitute for clinical assessment of an individual.
Can a rapid HBsAg test show how active or severe the infection is?
No. Standard point-of-care HBsAg tests are qualitative and report only Reactive or Non-reactive. They do not measure viral load, liver function or disease stage. Quantitative HBsAg levels, HBV DNA and other markers are measured by laboratory methods, not by the rapid card.
Why might a rapid HBsAg test give a non-reactive result in someone who has hepatitis B?
A non-reactive result can occur during the early window period before antigen rises, when antigen is at very low levels, or with certain surface-antigen escape variants. Because sensitivity is below 100 percent for many rapid kits, a non-reactive result that does not fit the clinical picture should be reviewed and may warrant laboratory testing per local protocol.