Sandwich enzymoimmunoassay of hepatitis B surface antigen (HBsAg).

. A sandwich enzymoimmunoassay (EIA) procedure was developed for the detection of HBsAg using Fab' of anti-HBsAg conjugated with β-D-galactosidase from Escherichia coli with anti-HBsAg-coated silicone rubber discs as a solid phase. EIA could detect 1 ng/ml of HBsAg. It was as sensitive as radioimmunoassay (RIA, AusRia II) and about 30-fold more sensitive than reversed passive hemagglutination assay RPHA, ReverseCell). EIA and RIA could detect more HBsAg-positive sera than RPHA.