International collaborative study on the 3rd WHO International Standard for hepatitis B surface antigen.

•The WHO International Standard (IS) for hepatitis B surface antigen (HBsAg) is used to standardize HBsAg assays.•A WHO international collaborative study involving 12 laboratories from 9 countries calibrated the 3rd IS for HBsAg in International Units (IU).•The 3rd IS was prepared from plasmas collected in Vietnam and is HBV subgenotype B4 with a heterogeneous HBsAg subtype population of ayw1 and adw2.•Consistent with previous studies, specific subgenotype differences may be observed.•The WHO Expert Committee on Biological Standardization established the 3rd IS for HBsAg in October 2014 with a potency of 47.3 IU per ampoule.