Hepatitis-associated markers in the American Red Cross volunteer blood donor population. ii. Distribution of level of HBsAg reactivity by radioimmunoassay and occurrence of nonspecific reactivity.

During the year 1978 this laboratory evaluated the specificity of all samples found reactive for hepatitis B surface antigen (HBsAg) by 44 of 57 regions of the American Red Cross Blood Services. Radioimmunoassay detected a total of 1.921 HBsAg-reactive sampled among more than three million donor units tested. A vast majority (96%) of the samples had high level of HBsAg (greater than or equal to 20 ng/ml). Only about 50% of the samples with low level of HBsAg (less than 20 ng/ml) were reactive in reversed passive hemagglutination. There were 13 samples that were repeatable for HBsAg but were considered nonspecific as they were nonneutralizable in radioimmunoassay, 2 donors who showed nonspecific reactivity were further tested and it was found that the reactivity in radioimmunoassay persisted for more than 9 months, and this reactivity was also detectable by a second commercial kit for HBsAg. Antibodies to core and surface antigen were not found in any of the nine samples that were tested. The explanation of this nonspecific reactivity is unclear, but the data suggest that the nonspecific factor(s) may be an inherent property of the sample rather than a deficiency of the test reagents.