Evaluation of alternative counting methods for radioimmunoassay of hepatitis-associated antigen (HB-Ag).

Alternative counting methods for the Abbott “AusR1A” hepatitis-associated antigen test have been devised and evaluated. These methods involve solubilization of the tube-bound radiolabeled complex with glacial acetic acid, transfer of the eluate to a counting vial of choice, and measurement by either a gamma scintillation or a liquid scintillation system. These methods, when compared to the direct counting of the AusRIA tube for sera from more than 250 patients and controls, gave a correlation coefficient of 0.94 to 0.99. iodine-125 counting efficiencies averaged 65% both for direct counting of the AusRIA tube and for gamma counting of the eluate. By liquid scintillation counting, iodine-i 25 counting efficiency averaged 50%. This method avoids high background, chemiluminescence, and quench, and is easy to perform. By using glacial acetic acid to solubilize the labeled material, the eluate can be counted by various types of gamma counters as well as by liquid scintillation systems.