Background and objectives: The availability of simple diagnostic methods may contribute to more efficient control of sexually transmitted diseases (STDs) in developing countries. For the detection of syphilis, a simple rapid plasma reagin (RPR) "teardrop" assay for finger-prick blood samples was developed in 1962. The reliability of this test is compared with RPR, Treponema pallidum hemagglutination assay (TPHA), and fluorescent treponemal antibody absorption (FTA-Abs) assays performed on venous blood samples.
Goal of this study: To evaluate the potential usefulness of the finger-stick RPR teardrop assay for diagnosis of syphilis in settings with poor medical resources.
Study design: Pregnant women evaluated at two health centers in Pikine, Senegal were tested for STDs. The RPR teardrop assay was performed on plasma from blood samples obtained by finger prick, and standard RPR, TPHA, and FTA-Abs procedures were performed on serum obtained by vein puncture.
Results: The sensitivity and specificity of the finger-prick RPR teardrop assay were 69.7% and 96.5%, respectively, and its reactivity was correlated with RPR serum antibody titer.
Conclusion: The finger-prick RPR teardrop assay is not a reliable alternative to the classic serum RPR test.
PIP: Health workers took finger-prick blood samples from at least 452 pregnant women at 2 health centers in Pikine, Senegal, to compare the effectiveness of the rapid plasma reagin (RPR) teardrop card test with that of the standard RPR 18 mm circle card test. Specifically, the researchers wanted to evaluate the RPR teardrop card test's potential usefulness in diagnosing syphilis in areas with poor medical resources, such as developing countries. Just 23 of 48 (47.9%) women who had at least 1 reactive cardiolipin test had positive results for both tests. Among these 48 cases, the RPR teardrop card test correctly identified antibodies of Treponema palladium in 67.6% of cases (sensitivity) and 96.7% of cases who did not have these antibodies (specificity). Among the 402 sera specimens which did not react to the Treponema palladium hemagglutination (TPHA) assay, the RPR teardrop test had a positive predictive value of 97% (33 of 34 cases which reacted to the RPR 18 mm circle test). Among the 402 finger-prick plasma specimens, the plasma RPR teardrop card test correctly identified 388 pregnant women (i.e., specificity, 96.5%) who did not have T. palladium antibodies and 23 of the 33 women (i.e., sensitivity, 69.7%) who did indeed have T. palladium antibodies according to RPR and TPHA results. Its positive predictive value was 62% (23 of the 37 who had a reactive RPR teardrop test). A significant correlation existed between the RPR serum titer and the reactivity of the RPR teardrop test on plasma (p = .005). These findings showed that the RPR 18 mm circle card test performed on serum is a more accurate diagnostic test than the RPR teardrop card test. Thus, the researchers did not recommend the RPR teardrop assay as an alternative to RPR 18 mm circle card test for diagnosing syphilis.