Quantitative evaluation of the FTA-ABS-IgM and VDRL test in treated and untreated syphilis

Observations made on fluorescent treponemal antibody absorption (FTA-ABS) immunoglobulin M (IgM) titres in patients with untreated early syphilis showed non-reactive or weakly reactive results in patients with primary (one of five cases) and secondary (two of 16 cases) lesions. In patients with primary (19.5%) and secondary (15%) syphilis sera remained reactive with increased titres for more than one year after treatment. The respective figures in the results of the Venereal Disease Research Laboratory (VDRL) test were zero in primary and 20% in secondary syphilis. The non-reactive FTA-ABS IgM results may possibly be explained by competitive inhibition of IgM by immunoglobulin G (IgG). The persistence of reactivity in a comparable percentage has been observed by other investigators (Grin et al., 1974; Wilkinson and Rodin, 1976). The current results therefore suggest that FTA-ABS IgM titres are less reliable for assessing the effect of treatment than the course of the VDRL titres. The phenomenon of a decrease in FTA-ABS IgM titres soon after treatment with a later rise before final non-reactivity is a matter for further investigation.