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Factor V Resistance to Activated Protein C (APC)

By

Joel L. Moake

, MD, Baylor College of Medicine

Last full review/revision Aug 2019| Content last modified Aug 2019
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Topic Resources

Mutations of factor V make it resistant to its normal cleavage and inactivation by activated protein C, and they predispose to venous thrombosis.

Activated protein C (APC), in complex with protein S, degrades coagulation factors Va and VIIIa, thus inhibiting coagulation (see figure Pathways in blood coagulation). Any of several mutations to factor V make it resistant to inactivation by APC, increasing the tendency for thrombosis.

Factor V Leiden is the most common of these mutations. Homozygous mutations increase the risk of thrombosis more than do heterozygous mutations.

Pathways in blood coagulation

Pathways in blood coagulation

Factor V Leiden as a single gene defect is present in about 5% of European populations, but it rarely occurs in native Asian or African populations. It is present in 20 to 60% of patients with "spontaneous" venous thrombosis.

Diagnosis

  • Plasma coagulation assay

Diagnosis is based on

  • A functional plasma coagulation assay (eg, the failure of patient's plasma partial thromboplastin time [PTT] to become prolonged in the presence of snake venom–activated patient protein C)

  • Analysis of the factor V gene

Treatment

  • Anticoagulation

Anticoagulation with parenteral heparin or low molecular weight heparin, followed by oral warfarin, is used for venous thrombosis or for prophylaxis for patients at increased thrombotic risk (eg, by immobilization, severe injury, surgery).

It is probable, but not yet certain, that the direct oral anticoagulant (DOAC) inhibitors of either thrombin (dabigatran) or factor Xa (eg, rivaroxaban, apixaban) can be used in place of warfarin for this disorder.

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