Comparison of performance of two Treponema pallidum automated chemiluminescent immunoassays in blood donors.

The recrudescence of syphilis is leading to the development of new serological tests. The goal of this study was to compare the performance of the more recent Elecsys Syphilis assay, the Electro Chemiluminescence Immunoassay (ECLIA), with the former Architect Syphilis TP assay, the Chemiluminescent Microparticle Immunoassay (CMIA), for the detection of antibodies against Treponema pallidum in blood donors. Serum samples of 5543 voluntary blood donors were screened in parallel with two tests. All repeatedly reactive (RR) samples by one or both assays were further analysed for confirmation by immmunoblot INNO-LIA and TPHA. Of 32 RR samples by CMIA, 21 were confirmed positive; of 21 RR samples by ECLIA, 20 were confirmed positive. The sensitivities of CMIA and ECLIA were 100% and 95.24% (95% CI = 85.71-100), respectively, not significant (p > 0.05). The specificity and predictive positive value (PPV) of CMIA were 99.86% (95% CI = 99.74-99.94) and 72.41%, respectively, while the specificity and PPV of ECLIA were both 100%, being statistically significant (p = 0.01 for both). The overall agreement was 99.80% and the Cohen's kappa coefficients was 0.79. In conclusion, the recent Elecsys Syphilis assay could represent another reliable assay for blood donor screening.