A coated-tube radioimmunoassay (FRC-RIA) for hepatitis B surface antigen.

A sandwich-type solid phase radioimmunoassay, FRC-RIA (Finnish Red Cross-RIA) for hepatitis B surface antigen (HBsAg) is described. Polystyrene test tubes coated with sheep anti-HBs gamma-globulin serve as the solid phase. The technique is specific and has a sensitivity of about 1 ng/ml for the subtypes ad and ay of HBsAg when corresponding subtype-specific antibodies are used as reagents. The total incubation time can be shortened from over 20 h to 3 h, with almost equal sensitivity, when the incubation temperature is raised from room temperature to 45 degrees C. The test is economical in reagents and is applicable to routine use.