[HBs antigen screening with Groupamatic. Inhibition of passive hemagglutination and latex test].

Some agglutination tests for HBs Ag and anti-HBs detection may be easily automated. Reverse hemagglutination, needing a lengthy incubation and several steps to carry out is unfit for Groupamatic, but hemagglutination inhibition and latex agglutination may be used. Hemagglutination inhibition using selected human red cells (ORh+) coated with cesium chloride purified HBs Ag, has been now routinely used at the C.N.T.S. with visual reading for almost 2 years. Negative and positive controls are necessary. The anti-HBs serum utilized has to be checked daily to get sensitive detection. Every new batch of coated red cells (valid 4 to 6 weeks) is checked in microtiter plates in the laboratory, before being used on Groupamatic. Both positive and dubious results are systematically retested in RIA. We found only 0,5% of false positive. The sensibility of the test compared favourably with other third generation test as reverse hemagglutination. It was close to the results obtained with radio-immuno-assay or enzyme-immuno-assay and it was more sensitive than counter-immuno electrophoresis. 65,472 samples were tested in parallel: we were able to detect 97% of HBs Ag detected by RIA. False negative results were less than 1 per 10 000 and may be avoided by using citrated solution for the anti-HBs serum dilution (suppression of auto-agglutination of the red cells). Antigex TG (the most active batch of latex coated with guinea pig, anti-HBs antibody) made by Pfizer, gave good results on Groupamatic and automatic reading was possible. But more results are necessary using various batches, before to recommend such reagent.