[Anti-HIV antibody screening kits and the difficulties of serology. Retrovirus Working Group of the Société Française de la Transfusion Sanguine].

The combined HIV1 + HIV2 assays allow to screen simultaneously the subjects infected by HIV1 or by HIV2 (About 80 HIV1 for 1 HIV2 in blood donations in France). An improvement of both sensitivity and specificity was obtained by using artificial proteins which have been selected for having the most immuno-dominant epitopes. The sensitivity is defined by the study of samples from recent and very recent seroconverters and the specificity by testing 2000 unselected blood donors. All the early seroconversions must be recognized as positive and less than 0.5% false positive results must be found in blood donors. HIV1 variants, temporarily named sub-type O have brought a new difficulty to the HIV serology, due to a weak homology, especially in "env" domains, between these variants and the reference HIV1 strains. Subjects living in France and infected by this HIV1 variant seem rare and the screening assays which miss some of these infected individuals seem capable to modify their reagents in order to recognize all of them.