Objectives: To evaluate the performance of a Russell viper venom-based activated protein C resistance (APCR) screening test relative to DNA analysis for the factor V Leiden mutation.
Methods: We evaluated the concordance between Pefakit APCR screening results and DNA analysis for 435 patients homozygous (n = 11), heterozygous (n = 310), or wild-type (n =114) for the G1691A allele.
Results: Using receiver operating characteristic analysis, we found that a cutoff of 1.89 for the APCR ratio yields a sensitivity and specificity of 99.1%. In patients with discrepant genotype-phenotype correlation, their APCR may provide a more clinically relevant result.
Conclusions: We compared several strategies for employing reflex testing and found that performing initial APCR screening followed by confirmatory molecular analysis on a subset of cases in the borderline regions between the diagnostic groups can reduce unnecessary testing by approximately 80% without compromising diagnostic accuracy.
Keywords: Activated protein C resistance; Factor V Leiden; Screening assays; Venous thromboembolism.