Analytical performance of the endogenous thrombin potential–based activated protein C resistance assay on the automated ST Genesia system

Background: The evaluation of activated protein C (APC) resistance based on the endogenous thrombin potential (ETP) is recommended during the development of steroid contraceptives in women. In 2019, this assay was validated on the calibrated automated thrombogram (CAT) device. However, in view of its screening potential, its automation is essential. Objectives: To transfer the ETP-based APC resistance assay on the ST Genesia system using reagent STG-ThromboScreen with exogenous APC added. Method: Dose-response curves were performed to define APC concentration leading to 90% ETP inhibition on healthy donors. Intra- and interrun reproducibility was assessed. The normal range was defined on the basis of 56 samples from healthy individuals. The sensitivity was assessed on 40 samples from women using combined oral contraceptives (COCs). A method comparison with the validated ETP-based APC resistance on the CAT system was performed. Results were expressed in normalized APC sensitivity ratio (nAPCsr). Results: The APC concentration leading to 90% ETP inhibition was 652 mU/mL. Intra- and interrun reproducibility showed standard deviation <4%. The nAPCsr normal range stood between 0.00 and 2.20. Analyses of 40 samples from women using COCs confirmed the good sensitivity of the assay. Compared to the CAT system, nAPCsr values were slightly higher on the automated system. Conclusion: This study is the first reporting the analytical performances of the ETP-based APC resistance assay on an automated platform. Results support the concept that this test, when incorporated into clinical routine, could become a promising regulatory and clinical tool to document on the thrombogenicity of female hormonal therapies.