Evaluation of the qualitative and automated quantitative microhemagglutination assay for antibodies to Treponema pallidum.

Qualitative and quantitative microhemagglutination assays for antibodies to Treponema pallidum (MHA-TP) were performed on 314 syphilitic and 597 presumably nonsyphilitic sera, and the results were compared with those of the fluorescent treponemal antibody-absorbed (FTA-ABS), the Treponema pallidum immobilization (TPI), and the Veneral Disease Research Laboratory (VDRL) tests. MHA-TP sensitivity was similar to that of the other tests in all stages of syphilis except primary syphilis, in which MHA-TP reactivity was only 64% compared with 82% in the FTA-ABS test, 73% in the VDRL test, and 67% in the TPI test. MHA-TP specificity was satisfactory and comparable to that of the other treponemal tests. Quantitation of the MHA-TP test was automated by use of Autotiter II equipment. Titers tended to become elevated later in the course of syphilis and to remain elevated longer than did VDRL titers. Reproducibility of the quantitative MHA-TP test was satisfactory, with duplicate tests agreeing within one doubling dilution on 97.5% of 351 reactive sera. Poor reproducibility was obtained with sera giving minimal reactions in the qualitative test, and such sera should be routinely retested. The MHA-TP is less time-consuming and costly than the FTA-ABS test and could be used in conjunction with the VDRL or another reagin test for syphilis to eliminate a large number of the FTA-ABS tests now required.