An evaluation of the relative sensitivities of the venereal disease research laboratory test and the Treponema pallidum particle agglutination test among patients diagnosed with primary syphilis.

BACKGROUND Because definitive methods for diagnosing primary syphilis are limited, it is important to optimize the sensitivity of serodiagnosis. OBJECTIVE To determine the most sensitive testing approach to the diagnosis of primary syphilis, using the commonly available serologic tests: the Venereal Disease Research Laboratory (VDRL) test and the Treponema pallidum particle agglutination (TP-PA) test. METHODS Sensitivities of 2 serologic testing strategies for primary syphilis were compared among 106 darkfield-confirmed cases treated in San Francisco from January 2002 through December 2004. RESULTS The sensitivity of the diagnostic strategy using VDRL confirmed by TP-PA was 71% (95% CI, 61%-79%). Substituting Rapid Plasma Reagin test for VDRL in a subset of 51 patients produced the same sensitivity (71%; 95% CI, 56%-83%). The sensitivity of TP-PA as the first-line diagnostic test was 86% (95% CI, 78%-92%). The sensitivity of the former approach was significantly lower among HIV-positive patients, compared with HIV-negative patients (55% vs. 77%, P = 0.05). CONCLUSIONS The TP-PA test as the first-line diagnostic test yielded higher sensitivity for primary syphilis than did the use of the currently recommended strategy.