Detecting APC-resistant factor V: a functional method without plasma dilution

A method for detecting activated protein C (APC)-resistant factor V, especi ally factor V Leiden, is described, which uses reagents containing two unfr actionated snake venoms. The procedure can be used for testing plasma sampl es from patients receiving oral anticoagulant therapy, heparin therapy and patients with lupus anticoagulant, and does not require the use of factor-V -deficient plasma. The sample plasma is first incubated with dilute venom f rom Agkistrodon contortrix contortrix (Southern Copperhead) which activates the endogenous protein C and then a dilute Russell's viper venom time test is performed. In individuals with APC-resistant factor V, especially facto r V Leiden, a marginal prolongation of dilute Russell's viper venom time wa s noted [1.14 +/- 0.14 s (n = 16)]. Non-carriers were ea:lily discriminated in each patient group, with a prolongation of 2.69 +/- 0.30 s for normal b lood donors (n = 127), 2.61 +/- 0.38 s for patients taking oral anticoagula nts (n = 102), 2.41 +/- 0.45 s for patients taking heparin (n = 96), and 2. 38 +/- 0.41 s for patients with lupus anticoagulant (n = 22). Patients taki ng oral anticoagulants with moderate prolongation (between 1.5- and 2.0-fol d) may have low levels of functional protein C and this might additionally indicate a subgroup of such patients at higher than normal thrombotic risk. Blood Coag Fibrinol 10:359-366 (C) 1999 Lippincott Williams & Wilkins.