Evaluation of a digital flocculation reader for the rapid plasma reagin test for the serological diagnosis of syphilis.

We described the ASiManager-AT digital flocculation reader to demonstrate concordance between visual and digital readings of the rapid plasma reagin test for detection of antibodies in the serum of patients with syphilis. A qualitative and quantitative rapid plasma reagin was performed on each serum samples giving a concordance of 98.6% and 99.7%, respectively, for reactives and 100% for nonreactives.

Novel point-of-care test for simultaneous detection of nontreponemal and treponemal antibodies in patients with syphilis.

We describe a point-of-care immunochromatographic test for the simultaneous detection of both nontreponemal and treponemal antibodies in the sera of patients with syphilis that acts as both a screening and a confirmatory test. A total of 1,601 banked serum samples were examined by the dual test, and the results were compared to those obtained using a quantitative rapid plasma reagin (RPR) test and the Treponema pallidum passive particle agglutination (TP-PA) assay. Compared to the RPR test, the reactive concordance of the dual test nontreponemal line was 98.4% when the RPR titers of sera were ≥1:2 and the nonreactive concordance was 98.6%. Compared to the TP-PA assay, the reactive and nonreactive concordances of the treponemal line were 96.5% and 95.5%, respectively. These results indicate that the dual test could be used for the serological diagnosis of syphilis in primary health care clinics or resource-poor settings and therefore improve rates of treatment where patients may fail to return for their laboratory results.

Defibrination of blood plasma for use in serological tests for syphilis.

Syphilitic plasma can be salvaged from discarded blood donations and converted to serum by defibrination. Sixty-nine units of plasma were treated with a stock solution of 100 U of thrombin per ml in 1 M calcium chloride and then with a 10% (wt/vol) solution of kaolin. Fibrinogen concentrations detected in initial plasma samples ranged from 94 to 4970 mg/liter (mean, 2532 mg/liter) for samples that were reactive by the rapid plasma reagin circle card test (RPR) and from 314 to 2742 mg/liter (mean 1528 mg/liter) for samples that were not reactive by the RPR. The treated samples showed no measurable fibrinogen remaining after the defibrination process. In the nontreponemal RPR for syphilis, 86% of the treated plasma samples retained the same endpoint titer as that of the initial plasma sample. When the Treponema pallidum passive-particle-agglutination test was used, 98% retained the same reactivity. In the Captia Syphilis-G enzyme immunoassay, 89% of the treated samples demonstrated no change in reactivity index, and in the fluorescent treponemal antibody absorption test, 96% showed no reduction in fluorescence. Human sera containing antibodies to syphilis are used at the Centers for Disease Control and Prevention for the preparation of reference controls or as samples for proficiency testing. Finding reactive sera is becoming more difficult due to the general decline of syphilis cases in the United States. The decreasing availability of these sera can be alleviated by salvaging plasma and converting it to serum.