Strengthening STD Screening Programs: Comprehensive Evaluation of High-Throughput Immunoassays for HIV and Syphilis Detection

Fourth-generation immunoassays are widely used for HIV and syphilis screening; however, false-reactive results may increase confirmatory testing and operational burden in high-throughput laboratories. This study evaluated the comparative performance of automated chemiluminescent immunoassays (MAGLUMI® HIV Ab/Ag Combi (Snibe Diagnostics Co. Ltd., Shenzhen, China), VITROS® ECiQ HIV Combo (Ortho Clinical Diagnostics, Raritan, NJ, USA), MAGLUMI® Syphilis (Snibe Diagnostics Co. Ltd., Shenzhen, China), and ARCHITECT® Syphilis TP (Abbott Diagnostics, Abbott Park, IL, USA) within a routine diagnostic algorithm, incorporating antibody differentiation immunoassays (INNO-LIA® HIV I/II Score (Fujirebio Europe N.V., Ghent, Belgium) and HIV-1 RNA PCR where applicable. A total of 240 archived serum samples for HIV testing and 180 for syphilis testing were analyzed. Agreement-based performance measures including sensitivity, specificity, overall percent agreement (OPA), and Cohen’s kappa (κ) were calculated as comparator-based estimates reflecting concordance within the routine diagnostic algorithm rather than absolute diagnostic accuracy against a universal reference standard. For comparisons with HIV-1 RNA PCR, positive and negative concordance rates are reported to reflect agreement between assays detecting different biological targets. Among samples with definitive (positive or negative) results, the MAGLUMI® HIV Ab/Ag Combi assay showed complete agreement with INNO-LIA® HIV I/II Score (κ = 1.00) and high agreement with PCR within the ARCHITECT® HIV Ag/Ab Combo-reactive subset (κ = 0.90). The VITROS® ECiQ HIV Combo assay demonstrated high agreement with INNO-LIA® HIV I/II Score (κ = 0.916) and substantial agreement with PCR (κ = 0.715), with a lower negative concordance rate with PCR observed in the ARCHITECT-reactive subset. A parallel five-modality analysis of 11 discordant samples applying the CDC 2014 algorithm demonstrated that all three immunoassay platforms successfully detected confirmed HIV-seropositive individuals with controlled viremia despite negative PCR, while MAGLUMI® HIV Ab/Ag Combi produced fewer false-reactive results than both ARCHITECT® and VITROS® in this discordant subset. Additionally, two cases showed INNO-LIA® indeterminate results with positive PCR, consistent with acute HIV infection during the early seroconversion stage; all three immunoassay platforms produced signals above the non-reactive threshold in both cases. For syphilis testing, both MAGLUMI® Syphilis and ARCHITECT® Syphilis TP assays showed complete agreement with INNO-LIA® Syphilis Score among samples with definitive results (κ = 1.00). In contrast, the RPR assay showed reduced positive predictive value (49.4%) and moderate agreement with INNO-LIA® Syphilis Score (κ = 0.52). Automated chemiluminescent immunoassay (CLIA) platforms demonstrated high agreement within a structured diagnostic algorithm in a high-throughput screening setting. Differences in assay performance were observed across platforms, particularly with respect to discordant results in the ARCHITECT-reactive PCR-evaluated subset for HIV and non-treponemal concordance for syphilis. These platforms may support more efficient laboratory workflows; however, findings should be interpreted within the context of comparator-based classification rather than absolute diagnostic accuracy.