Variation in the sensitivity of HBsAg screening kits

Fifteen HBsAg kits from 14 manufacturers were assessed. Their sensitivity was evaluated by testing 150 HBsAg-positive sera, sera from four donors who were low-level HBsAg carriers, and sequential specimens from 22 seroconverting individuals together with dilutions of six of these specimens. The British HBsAg Working Standard (0.5 IU mL^-1) and the NIBSC/UKBTS HBsAg Monitor Sample (0.125 IU mL^-1) were also tested. Five assays failed to detect one of the 150 routine HBsAg-positive sera. Four assays (Auszyme Monoclonal; Monolisa Ag HBs 2nd generation; Murex HBsAg; Ortho HBsAg Test Systems 3) were able to detect HBsAg in all but one of the six sera from low-level carriers, whereas one assay (MicroTrak II HBsAg) detected only one of the six. The most sensitive kit (Monolisa Ag HBs 2nd generation) detected H BsAg in 79 specimens from the seroconversion panels; four other kits detected HBsAg in at least 70 specimens, seven in 60 69, two in 50-59 and the least sensitive in 31. Further analysis of the findings on seroconverters indicated a median reduction in the duration of HBsAg detection of 5 days or more for four assays when compared with the most sensitive assay. One kit (Auszyme Monoclonal) detected HBsAg in 15 of the 18 dilutions prepared from the seroconversion specimens, whereas three kits detected HBsAg in fewer than 10 dilutions. Two kits gave negative reactions with the British HBsAg Working Standard on all of five occasions and six were consistently unreactive with the NIBSC/UKBTS HBsAg Monitor Sample; only three kits (Bioelisa, Enzygnost, Murex) were always reactive. There is therefore substantial variation in sensitivity among the HBsAg kits currently available.