[Serological confirmation of HIV infections in hospital practice: analysis of indeterminate western blot results].

Among 770 Western blots for HIV-1 confirmation on sera from subjects at high risk for HIV infection, 4.3% (33 cases) were indeterminate. Isolated, stable, reproducible anti-gp 160 reactivity, highly suggestive of a nonspecific reaction, was found in 16% of cases. There were three other probably nonspecific patterns with anti-gp 160 and either anti-gp 41 or anti-gp 120 reactivities and thin, atypical bands. Two patterns with anti-p24 and either anti-gp 160 or anti-gp 120 reactivities were consistent with HIV-1 seroconversion. Reactivity directed solely against gag products was seen in 18% of cases. The repeat test, performed in 16 cases, showed an identical pattern in 3 cases, a modified pattern in 3 cases, negative results in 9 cases, and seroconversion in 1 case. No case of HIV-2 infection was detected. Indeterminate Western blot results reflect nonspecific reactivity in most instances but should nevertheless lead to the exclusion of technical artefacts, seroconversion, and HIV-2 infection.