A COMPARISON BETWEEN 2 ACTIVATED PROTEIN-C RESISTANCE METHODS AS ROUTINE DIAGNOSTIC-TESTS FOR FACTOR-V-LEIDEN MUTATION

The most common commercially available test measuring activated protei n C (APC) resistance relies on the the anticoagulant response to added APC in an activated partial thromboplastin time (APTT) based method. Another method is a Russell Viper venom time (RVVT) based system. To i mprove the specificity for factor V Leiden of the APTT based method, p re-dilution of test plasma in FV-deficient plasma has recently been re commended. In this study we tested the relative suitabilities of the A PTT-based system, the RVVT-based system and their corresponding assays modified by pre-dilution in FV-deficient plasma, for screening asympt omatic subjects, a group of thrombophilic patients (in particular thos e with low APC ratios), patients on oral anticoagulants, and patients with lupus anticoagulant (LAC). We found the RVVT-based assay to be su perior to the APTT-based method in the separation of normals from thos e with FV Leiden mutation both in asymptomatic subjects and in the thr ombophilic patient group, Both modified assays demonstrated a sensitiv ity and specificity of 100% for FV Leiden, as verified by genotyping i n asymptomatic subjects, thrombophilic patients and patients on oral a nticoagulants, with the modified RVVT-based assay giving better separa tion between normals and FV Leiden. inhibition of phospholipid-depende nt coagulation by LAC antibodies rendered the APTT-based system less s uitable than the phospholipid-rich RVVT-based one, and as nine of the 20 LAC-positive patients were on warfarin, we showed only the modified RVVT assay to be a reliable predictor of factor V Leiden in this pati ent group.