Detection of hepatitis B surface antigen (HBS Ag) with use of alkaline phosphatase-labeled antibody to HBS Ag.

An enzyme-labeled "sandwich" assay was developed for the detection of the hepatitis B surface antigen (HBS Ag) with use of calf intestinal alkaline phosphatase and horse antibody to HBS Ag. It involved a total incubation time of 2.5 hr in three steps and was approximately equivalent in sensitivity to one of the commercially available radioimunoassays. The confirmatory test was of the neutralization type and required an additional 30-min incubation step. The enzyme-labeled antibody solution and the solid-phase antibody were extremely stable. They withstood storage at 2 C-8 C for longer than one year with virtually no decrease in activity. Accelerated tests of stability in storage at room temperature (20 C-24 C) showed only a small loss of potency over a one-year period. Three specimens were encountered that were confirmably positive by enzyme-labeled immunoassay but negative by radioimmunoassay.