Diagnostic performance of Treponema pallidum particle agglutination tests against electrochemiluminescence immunoassays for the detection of anti-TP antibodies: Evaluation study

Objectives Although the burden of syphilis is slightly increasing worldwide, there are a limited number of rapid, simple-to-use, accurate and cost-effective diagnostic tools available. Thus, we aimed to determine the diagnostic performance of the Treponema pallidum particle agglutination (TPPA) test (hereafter called index test) against an electrochemiluminescence immunoassay (ECLIA) (hereafter called reference test). We selected the available treponemal reference test (ECLIA) to evaluate the index test (TPPA) which is not currently in use in Ethiopia.Methods We conducted a multicentre cross-sectional study to evaluate the diagnostic performance of the index test against the reference test. We enrolled 581 syphilis-suspected cases from the five selected health facilities in Addis Ababa in this study. We collected data on sociodemographic and clinical characteristics and whole blood from each participant. We estimated the sensitivity, specificity and positive and negative predictive values of the index test.Results Of the 581 participants, 380 (65.4%) were female. The mean age of the participants was 39.7 years (+/- SD 16.6), with an age range of 18-94 years. The sensitivity of the index test was 99.4% (95% CI 96.4% to 100%), while the specificity was 100%. The positive predictive value of the index test was 100%, and the negative predictive value was 99.8% (95% CI 98.4% to 100%). There was no invalid test result.Conclusions The diagnostic performance of TPPA for syphilis was equivalent to that of ECLIA. Thus, TPPA can be used for the diagnosis of syphilis at the health facility level equivalent to a reference test.