Pitfalls in the sensitivity of HBsAg detection.

A number of 1800 serum samples from apparently healthy subjects were tested by immunodiffusion (ID) and counterimmunoelectrophoresis (CIE) with a view to confirming the presence of HBsAg; results were uncertain in 21% of the cases. The enzyme immunoassay (ELISA kits) used to elucidate these uncertain reactions showed half of them to be negative. About 3% of the remaining sera, HBsAg-positive by ELISA, were positive by ID, but constantly negative by repeated CIE tests. Some possible explanations are suggested and the implications of such pitfalls in the interpretation of sero-epidemiological analyses are discussed.