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Syphilis: immunofluorescence reaction
Last reviewed: 06.07.2025
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Treponemal antibodies of the IgG class are not normally detected in blood serum.
The immunofluorescence reaction (FTA-ABS IgG) is related to treponemal tests for syphilis diagnostics, it allows to detect specific treponemal AT of class IgG in blood. The sensitivity and specificity of the test for primary syphilis is 85% and 97% respectively, for secondary syphilis - 99% and 97%, for late syphilis - 95% and 97%, for latent - 95% and 97%. FTA-ABS IgG is used to confirm the diagnosis if there is a suspicion of late syphilis of any type, it is necessary to conduct this test even in the case when MR is negative. Antibody titers in RIF do not correlate with the clinical activity of the disease and remain elevated indefinitely in 95% of patients, reflecting the presence of infection in the past. FTA-ABS IgG is not used to evaluate treatment, as the test remains positive for 2 years after adequate treatment in 80% of cases of seropositive early syphilis. Currently, the FTA-ABS IgG test is not recommended for the diagnosis of congenital syphilis in newborns.