'Aspira': a new sensitive assay for the detection of hepatitis B surface antigen.

A sensitive method for the detection of hepatitis B surface antigen (HBsAg) is described whereby the separation of specific antibody by affinity chromatography is incorporated into one of the assay reagents. HBsAg, which may be obtained from tissue culture fluids of a human hepatoma cell line, is first reacted with polystyrene beads. Unoccupied spaces on the plastic are next covered with a non-specific protein (e.g. albumin). The plastic is then reacted with either whole antiserum or an IgG fraction of anti-HBs. Care must be taken to cover all of the reacting sites of the first layer of HBsAg with sufficient anti-HBs. This results in a reagent of detecting antigen. No affinity purified antibody was necessary because the reagent, at this stage, contains only specific antibody on the surface. Antigen reacting with this reagent can be detected by the addition of radioactively labeled IgG fraction of anti-HBs, which will complete the 'sandwich'. This assay has been evaluated and found to be as sensitive as those commerically available.