The role of treponemal tests in therapeutic decision making

As part of process evaluation of a syphilis control program, the predictability of serologic tests was assessed by reviewing the primary care case records (containing serology findings on 5,643 sera) of all individuals in six aboriginal communities. The direct relationship of predictability to positivity of treponemal test was influenced by the Venereal Disease Research Laboratory (VDRL) titre and when results were stratified by this variable, an inverse association of predictive value with levels of positivity of treponemal test was demonstrated. The predictive values positive of the FTA-ABS-IgM test for untreated disease was 0.31 for VDRL titres of 1:4 and increased to 0.84 for VDRL titres exceeding 1:16. The predictive value of treponemal tests would be increased by more restrictive criteria for their performance, and optimum interpretation demands concurrent assessment of VDRL titre, and clinical and epidemiological background of the individual patient. This type of evaluation on individual control programs is encouraged because the quantitative findings will vary with disease prevalence, testing criteria, and the individual laboratory testing performance.