Modified immunofluorescence test for the serologic diagnosis of gonorrhea (FGT-ABS)

Investigation of the source of false-positive reactions in the Fluorescent Gonococcal Test-Heated (FGT-H) implicated antibodies to antigens common to Neisseria gonorrhoeae and N. meningitidis. Absorption experiments proved that the fluorescence was due to both species-specific and common antigens and that in most cases the common antibodies could be successfully absorbed by a soluble protein extract of N. meningitidis. The value of such an absorption step was examined using sera from 500 women, 73 from bacteriologically confirmed cases of gonorrhea and 427 from bacteriologically and clinically negative cases. The absorption step reduced the false positivity rate by 58% without a significant change in sensitivity. The modified procedure, the Fluorescent Gonococcal Antibody Test-Absorbed (FGT-ABS), has a sensitivity similar to the Fluorescent Gonococcal Test-Heated (FGT-H) but has the advantage of higher specificity.