Serological evidence of presence of HBsAg undetectable by conventional radioimmunoassay in anti-HBc positive blood donors.

Sera from two blood donors, one of whom was implicated in a case of post-transfusion hepatitis B, were found to be positive for anti-HBc and negative for HBsAg by conventional radioimmunoassay and were retested for HBsAg after concentration (pepsin digestion and polyethylene glycol precipitation). The presence of occult HBsAg was confirmed in both. These observations have implications for blood transfusion, and wider studies of anti-HBc in blood donors are recommended before the introduction of routine screening for anti-HBc and exclusion of the positive donors from blood donation.