From the Guidelines
No, the activated Partial Thromboplastin Time (aPTT) would typically not be elevated in a patient with Factor V Leiden. Factor V Leiden is a genetic mutation that makes Factor V resistant to inactivation by activated protein C, resulting in a hypercoagulable state that increases the risk of venous thromboembolism. Despite this hypercoagulability, routine coagulation tests like aPTT and PT (Prothrombin Time) usually remain normal in these patients. This occurs because Factor V Leiden doesn't reduce clotting factor levels or impair the coagulation cascade; rather, it enhances coagulation by allowing Factor V to remain active longer than normal.
Key Points to Consider
- The aPTT test is not specific for Factor V Leiden and can be influenced by various factors, including acute phase reactants, pregnancy, and oral contraceptives 1.
- The traditional functional test based on aPTT lacks specificity for Factor V Leiden and is subject to perturbation by several clinical factors 1.
- To diagnose Factor V Leiden, specific tests are required, including an activated protein C resistance assay as a screening test, followed by genetic testing to confirm the presence of the mutation 1.
- These specialized tests, rather than routine coagulation studies, are essential for proper diagnosis of this common inherited thrombophilia.
Diagnosis and Testing
The diagnosis of Factor V Leiden requires specific testing, including an activated protein C resistance assay and genetic testing. The activated protein C resistance assay is a functional test that measures the ability of activated protein C to inactivate Factor V. Genetic testing can confirm the presence of the Factor V Leiden mutation.
Clinical Implications
The presence of Factor V Leiden has significant clinical implications, including an increased risk of venous thromboembolism. Patients with Factor V Leiden may require lifelong antithrombotic prophylaxis, particularly after a thrombotic event. Asymptomatic family members may also wish to determine their Factor V Leiden status to guide antithrombotic prophylaxis during periods of risk.
From the Research
Coagulation Tests in Factor V Leiden
- The activated Partial Thromboplastin Time (aPTT) is a coagulation test that measures the time it takes for blood to clot 2.
- Factor V Leiden is a genetic disorder that affects the coagulation system, increasing the risk of venous thromboembolism 2.
- The aPTT test is not typically used to diagnose Factor V Leiden, as it is not sensitive to the defect 2.
- The diagnosis of Factor V Leiden usually requires the activated Protein C resistance assay or DNA analysis of the F5 gene 2.
Effect of Factor V Leiden on Coagulation Tests
- Factor V Leiden can affect the results of coagulation tests, but its impact on aPTT is not significant 3.
- The prothrombin time (PTT) and international normalized ratio (INR) may be more relevant in monitoring patients with Factor V Leiden who are on anticoagulant therapy 4.
- The aPTT may be normal or slightly elevated in patients with Factor V Leiden, but this is not a reliable indicator of the presence or absence of the mutation 5.
Clinical Implications
- The management of patients with Factor V Leiden requires a comprehensive approach, including coagulation testing, genetic analysis, and clinical evaluation 6.
- The decision to test for Factor V Leiden should be based on individual patient risk factors and clinical presentation 6.
- Patients with Factor V Leiden may require long-term anticoagulation to prevent recurrent venous thromboembolism, but the optimal duration and intensity of therapy are still debated 4.