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Diagnostic Tests – Factor V Leiden Mutation
1. What Is Factor V Leiden?
Factor V Leiden is a genetic mutation that makes Factor V resistant to the inhibitory action of activated protein C (APC), one of the body’s natural anticoagulants. Normally, protein C slows the clotting cascade by inactivating Factor V; however, the Factor V Leiden mutation alters the structure of Factor V so that it no longer responds effectively to protein C. As a result, clotting continues unchecked, creating a hypercoagulable state. This condition is the most common inherited thrombophilia, significantly increasing a person’s risk of developing venous thromboembolism (VTE) such as deep vein thrombosis (DVT) or pulmonary embolism (PE).
2. When Do You Answer Factor V Leiden Mutation Testing?
Testing for the Factor V Leiden mutation is indicated in young patients who present with an unprovoked DVT or PE, especially when the event occurs without clear provoking factors such as recent surgery, trauma, or immobilization. Board-style scenarios often feature:
In these cases, Factor V Leiden testing is the most accurate test for identifying a hereditary cause of hypercoagulability. It is part of the evaluation when considering inherited thrombophilias.
3. What Other Tests Should Be Sent With It?
When evaluating a patient for possible inherited or acquired hypercoagulable states, several additional tests are typically ordered alongside Factor V Leiden. These include:
Together, these tests help create a comprehensive picture of a patient’s thrombotic risk and identify whether the cause is inherited, acquired, or multifactorial.
1. What Is Factor V Leiden?
Factor V Leiden is a genetic mutation that makes Factor V resistant to the inhibitory action of activated protein C (APC), one of the body’s natural anticoagulants. Normally, protein C slows the clotting cascade by inactivating Factor V; however, the Factor V Leiden mutation alters the structure of Factor V so that it no longer responds effectively to protein C. As a result, clotting continues unchecked, creating a hypercoagulable state. This condition is the most common inherited thrombophilia, significantly increasing a person’s risk of developing venous thromboembolism (VTE) such as deep vein thrombosis (DVT) or pulmonary embolism (PE).
2. When Do You Answer Factor V Leiden Mutation Testing?
Testing for the Factor V Leiden mutation is indicated in young patients who present with an unprovoked DVT or PE, especially when the event occurs without clear provoking factors such as recent surgery, trauma, or immobilization. Board-style scenarios often feature:
- A first-time clot in a young adult
- A thrombotic event after a long airplane flight or prolonged immobility
- A family history of recurrent clots
In these cases, Factor V Leiden testing is the most accurate test for identifying a hereditary cause of hypercoagulability. It is part of the evaluation when considering inherited thrombophilias.
3. What Other Tests Should Be Sent With It?
When evaluating a patient for possible inherited or acquired hypercoagulable states, several additional tests are typically ordered alongside Factor V Leiden. These include:
- Protein S levels – Low levels increase clotting risk.
- Protein C levels – Especially important when the case mentions skin necrosis, which may occur when patients with undiagnosed protein C deficiency receive warfarin.
- Lupus anticoagulant testing – Consider this when the patient has an unexplained prolonged PTT, recurrent spontaneous abortions, or autoimmune features; this suggests antiphospholipid syndrome.
- Antithrombin III deficiency testing – Suspect this when a patient shows resistance to heparin, as AT III is required for heparin’s anticoagulant effect.
Together, these tests help create a comprehensive picture of a patient’s thrombotic risk and identify whether the cause is inherited, acquired, or multifactorial.
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