High sensitivity and specificity of a coagulation assay for the detection of heterozygous and homozygous factor V Leiden--based resistance to activated protein C.

To the Editor: 70 nmol/L, 35 nmoUL, 14 nmollL, 7 nmol/L, and 0 nmol/L APC, corresponding to loo%, 50%, 20%, lo%, and 0% factor Va inactivaResistance to activated protein C (APC). caused by a mutated tion, respectively. Here we will summarize our current experience Coagulation factor v (factor v Leiden), has been reported as a prediswith this modified functional assay for the detection of factor V posing factor in a large fraction of patients with venous thromboemLeiden, bolism. Diagnosis of APC resistance is currently based upon measursamples from 197 patients with thrombotic disorders (including 1% the ratio of activated Partial thromboplastin times ( A m s ) in the patients receiving heparin or oral anticoagulants) were evaluated for Presence and absence of exogenous APC. However, determination the presence of the factor V Leiden mutation using the polymerase of this APC resistance ratio is not reliable in patients receiving chain reaction followed by digestion of amplification products with anticoagulant therapy. In their recent review of inherited thrombo~ ~ f l and detection of a restriction fragment length polymorphism philia in Blood, De Stefan0 et all cite unpublished observations as described by ~ ~ r t i ~ ~ et d.3 I~ all test plasmas APC resistance indicating that predilution Of the test plasma with factor V deficient was analyzed using a commercially available kit to determine the