Comparison of confirmation methods for hepatitis-B antigen and the nature of false-positives detected by 125I-immunoglobulins.

: Immunologic specificity associated with solid-phase direct radioimmunoassay (RIA) using guinea pig antibodies for HBsAg detection (Ausria-125TM) was examined further with physicochemical techniques. The RIA reactivities which could not be neutralized by wide-spectrum human anti-HBs serum appeared to be physically distinct from true HBsAg particles; hence, they were truly false-positive, resulting from immunologic cross-reactions. In order to ensure the full advantages of using this highly sensitive RIA test, a confirmatory test using specific human anti-HBs for neutralization is therefore required to distinguish the true- and false-positives. The basic RIA technique is a two-step procedure. Two basic confirmation procedures, namely, a first-step neutralization and a second-step neutralization, were investigated in depth to assess their efficacy and practicality for confirmation. Both procedures were effective for confirmation purposes; however, the first-step neutralization procedure failed to confirm some high-titered HBsAg samples unless these samples were appropriately diluted. The second-step neutralization method did not require dilutions of any test samples.