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

Abstract

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.

FIG. 1.

Structure of the Chembio dual POC test for syphilis showing the locations of the antigen lines. A, dissected view following testing of reactive serum; B, complete cassette following testing of reactive serum.

FIG. 2.

Dual POC syphilis tests showing patterns of reactivity and their interpretations.

FIG. 3.

Distribution of RPR titers among RPR-positive, TP-PA-positive sera obtained from the Georgia Public Health Laboratories and rates of seroreactivity of the nontreponemal line in the dual POC test.