The Factor V (Leiden) Test: Evaluation of an assay based on dilute RussellViper Venom Time for the detection of the Factor V Leiden mutation

In the present study a new clotting assay for the detection of an increased resistance of coagulation factor V against degradation by activated protei n C (Factor V Leiden mutation, FVLM) was evaluated. The Factor V (Leiden) T est (Gradipore. North Ryde NSW, Australia) is based on the dilute Russell V iper Venom Time (DRVVT, which is prolonged when the plasma sample is preinc ubated with dilute whole Agkistrodon contortrix contortrix venom for activa tion of protein C (PC). In contrast to the DRVVT based global assay, Protei n C Pathway Test (Gradipore, North Ryde NSW, Australia) this new assay is e xpected to be more specific for FVLM because of optimized amounts of the ve nom. The test result is expressed as the ratio between the DRVVT with and w ithout addition of the venom. The following precision values were found: in traassay coefficient of variation (CV): 5.53% (n=20) in the normal range, 4 .30% (n=20) in the pathological range; interassay CV: 6.90% (n=10) and 7.64 % (n=10), respectively. A normal range (5th to 95th percentile) of 2.12 to 3.08 was calculated from 50 healthy controls. A ratio below 2.12 was found in all samples from patients with FVLM (n=21), in 9 of 12 patients with PC, in 0 of 6 with protein S (PS), and in 0 of 4 with antithrombin (AT) defici ency. There was, however, a good discrimination between carriers of the FVL M (highest ratio 1.44) and patients deficient in PC (lowest ratio 1.59), in particular when samples were prediluted with factor V deficient plasma FVD P (1.16 vs. 1.96, respectively). Predilution of samples with FVDP caused a clear discrimination between controls and patients deficient in PC, PS, AT, and FVLM-positive individuals and also in patients on oral anticoagulant t reatment. Our data show that the Factor V (Leiden) Test discriminates well between carriers of the FVLM and healthy controls or patients deficient in PC, PS, and AT. Individuals presenting values between the lower cutoff of c ontrols and the range in which FVLM-positive individuals are found are high ly suspicious for protein C deficiency. (C) 1999 Elsevier Science Ltd. All rights reserved.