[Positive HBs antigen in the absence of hepatitis B virus infection].

French recommendations for the screening of hepatitis B virus (HBV) infection were updated in 2019 with the association of three markers: HBs Ag, anti-HBs Ab and anti-HBc Ab. These three markers allow identification of infected patients, vaccinated patients and patients who have been in contact with HBV. A positive HBs Ag is usually associated with HBV infection but this interpretation must take into account the clinical context. In particular, the absence of anti-HBc Ab, normal ALAT levels and the absence of jaundice can be associated with recent HBV vaccination or false-positive HBs Ag. Recent HBV vaccination can usually be confirmed by patient questioning, while confirmatory tests are useful to detect false positive HBs Ag. If necessary, a second sample can be requested to confirm the interpretation.