factor V Leiden (FVL, Leiden factor V, Mutation analysis)
المؤلف:
Kathleen Deska Pagana, Timothy J. Pagana, Theresa Noel Pagana.
المصدر:
Mosbys diagnostic and laboratory test reference
الجزء والصفحة:
15th edition , p401-402
2025-12-09
32
Type of test Blood
Normal findings
Negative for factor V Leiden
Test explanation and related physiology
Factor V is an important factor in reaction 4 (common path way) of normal hemostasis. The term factor V Leiden (FVL) refers to an inherited abnormal form of the gene for fac tor V. The endogenous anticoagulant protein C is normally able to break down factor V at one of these cleavage sites. However, protein C cannot inactivate this same cleavage site on FVL. Therefore FVL is inactivated at a rate approximately 10 times slower than that of normal factor V and persists longer in the circulation. This results in increased thrombin generation and a mild, hypercoagulable state reflected by elevated levels of pro thrombin fragment F1 + 2 and other activated coagulation markers. This test is used to diagnose FVL-associated thrombophilia.
Individuals heterozygous for the FVL mutation have a slightly increased risk for venous thrombosis. Homozygous individuals have a much greater thrombotic risk (e.g., deep vein thrombosis [DVT], arterial thrombosis, or pulmonary embolism).
Individuals who are candidates for FVL testing include patients who
• experienced a thrombotic event without any predisposing factors
• have a strong family history of thrombotic events
• experienced a thrombotic event before 30 years of age
• experienced DVT during pregnancy or while taking birth control pills
• had venous thrombosis at unusual sites (e.g., cerebral, mesenteric, portal, and hepatic veins)
• experienced an arterial clot
Testing for FVL is sometimes preceded by a coagulation screening test called the activated protein C (APC) resistance test. This test identifies resistance of factor V to APC. If APC resistance is identified, the patient then may choose to undergo mutation testing by DNA analysis of the F5 gene, which encodes the factor V protein. This testing should be accompanied by professional genetic counseling for the patient and family members.
Procedure and patient care
• See inside front cover for Routine Blood Testing.
• Fasting: no
• Blood tube commonly used: purple
• If the patient is having FVL mutation analysis, anticoagulants will not interfere with testing.
• As an alternative, genetic testing can be done on the patient’s cells obtained by a smear of the oral surface of the cheek.
• Remember: if the patient is receiving anticoagulants, the bleeding time will be increased.
Abnormal findings
- Activated protein C resistance
- Factor V Leiden genetic mutation (homozygous or heterozygous)
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