Factor V Leiden Diagnosis and Management
Introduction to Factor V Leiden
- The American College of Medical Genetics recommends that PT/INR is normal in patients with Factor V Leiden, as it does not affect the extrinsic or common coagulation pathways measured by PT/INR testing 1, 2
- Factor V Leiden involves a single point mutation (G1691A) that substitutes glutamine for arginine at position 506, making activated Factor V resistant to inactivation by activated protein C, which is not detected by standard PT/INR testing 3
Diagnostic Methods for Factor V Leiden
- Direct DNA-based genotyping or Factor V Leiden-specific functional assays are the recommended diagnostic methods, not PT/INR, according to the American College of Medical Genetics 1
- Modified activated protein C resistance (APC-R) assays using patient plasma diluted in Factor V-deficient plasma provide reliable differentiation between heterozygotes and homozygotes with minimal interference from other clinical factors 1
- Traditional aPTT-based functional tests cast a wider net but lack specificity and are subject to interference from acute phase reactants, pregnancy, oral contraceptives, lupus anticoagulant, heparin, and warfarin therapy, as stated by the American College of Medical Genetics 1
Anticoagulation Therapy in Factor V Leiden
- Patients on anticoagulation therapy should proceed directly to molecular testing if modified functional assays are not available, as standard coagulation tests cannot reliably detect Factor V Leiden in these circumstances, according to the American College of Medical Genetics 1
- The INR therapeutic range (2.0-3.0) for anticoagulation applies equally to patients with Factor V Leiden who develop venous thromboembolism, as moderate-intensity anticoagulation is adequate for these patients, as recommended by the American College of Chest Physicians 5