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

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Abstract
Observations made on fluorescent treponemal antibody absorption (FTA-ABS) immunoglobulin[Ig]M titers in patients with untreated early syphilis showed non-reactive or weakly reactive results in patients with primary (1 of 5 cases) and secondary (2 of 16 cases) lesions. In patients with primary (19.5%) and secondary (15%) syphilis sera remained reactive with increased titers for more than 1 yr after treatment. The respective figures in the results of the Venereal Disease Research Laboratory (VDRL) test were 0 in primary and 20% in secondary syphilis. The non-reactive FTA-ABS IgM results may possibly be explained by competitive inhibition of IgM by IgG. The persistence of reactivity in a comparable percentage was observed by other investigators. The current results therefore suggest that FTA-ABS IgM titers are less reliable for assessing the effect of treatment than the course of the VDRL titers. The phenomenon of a decrease in FTA-ABS IgM titers soon after treatment with a later rise before final non-reactivity is a matter for further investigation.