Longitudinal evaluation of HIV-1 LAg incidence assay and proficiency panel stability for external quality assurance.

Accurate HIV incidence estimates are essential for monitoring epidemic trends and evaluating prevention efforts. The limiting antigen (LAg) avidity enzyme immunoassay is the most widely used method to classify recent versus long-term HIV infections. The External Quality Assurance Oversight Laboratory (EQAPOL), in collaboration with Vitalant Research Institute, conducts a global External Quality Assurance (EQA) program to evaluate laboratory performance using commercial LAg kits. We assessed (i) the stability of calibrators and reagents from Sedia and Maxim kits over their shelf life, and (ii) the longitudinal consistency of EQA panel samples tested across nine proficiency rounds (2018-2023). Mixed-effects models were used to detect trends in optical density (OD) and normalized OD (ODn) values over time. No significant trends in OD or ODn were observed for either kit, and EQA panel samples showed stable reactivity across all rounds. Minor ODn shifts did not affect recency classification. Sedia kits consistently yielded slightly higher ODn values than Maxim kits, consistent with prior reports. These findings confirm the long-term reliability of both LAg assay kits and EQA panel materials, supporting the robustness of EQAPOL's quality assurance framework for accurate global HIV incidence surveillance.IMPORTANCEReliable estimation of HIV incidence depends on accurate classification of recent versus long-term infections, which in turn requires consistent assay performance and robust quality assurance. The External Quality Assurance Oversight Laboratory LAg External Quality Assurance program provides longitudinal monitoring of laboratory proficiency for two widely used commercial assays. By demonstrating the long-term consistency of calibrators, reagents, and quality control panels across multiple production lots and testing rounds, this study confirms the robustness of the global limiting antigen testing framework. These results strengthen confidence in the comparability of HIV incidence data across surveillance networks and geographic regions, supporting evidence-based decision-making for HIV prevention programs.