LAUSR

Objectives: To compare the accuracy and reliability of phenotypic activated protein C resistance (aPC‐R) assays with a genotypic assay for the factor V Leiden F5 p.R506Q (FVL) mutation. Methods: Data were obtained from an electronic data warehouse for FVL testing performed at an academic institution with a large referral laboratory service. In total, 1,596 patients were identified who had undergone both phenotypic aPC‐R and genotypic FVL mutation testing. Results: Phenotypic testing showed a high level of sensitivity, specificity, and other biostatistical values compared with genotypic testing. Improvements in technology decreased the amount of equivocal phenotypic results. Conclusions: Phenotypic assays had close to total concordance with genotypic assays over 16 years of testing. Changing ordering practices could result in up to an 80% reduction in testing costs.