Comparison of Phenotypic Activated Protein C Resistance Testing With a Genetic Assay for Factor V Leiden

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.