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Protein C Deficiency


Joel L. Moake

, MD, Baylor College of Medicine

Last full review/revision Jan 2021| Content last modified Jan 2021
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Because activated protein C degrades coagulation factors Va and VIIIa, deficiency of protein C predisposes to venous thrombosis.

Protein C is a vitamin K–dependent protein, as are coagulation factors VII, IX, and X; prothrombin; and proteins S and Z. Because activated protein C (APC) degrades factors Va and VIIIa, APC is a natural plasma anticoagulant. Decreased protein C due to a genetic or an acquired abnormality predisposes to venous thrombosis Deep Venous Thrombosis (DVT) Deep venous thrombosis (DVT) is clotting of blood in a deep vein of an extremity (usually calf or thigh) or the pelvis. DVT is the primary cause of pulmonary embolism. DVT results from conditions... read more Deep Venous Thrombosis (DVT) .

Heterozygous deficiency of plasma protein C has a prevalence of 0.2 to 0.5%; about 75% of people with this defect experience a venous thromboembolism (50% by age 50).

Homozygous or doubly heterozygous deficiency causes neonatal purpura fulminans, ie, a severe neonatal type of disseminated intravascular coagulation (DIC), which manifests with ecchymoses and extensive venous and arterial thromboses, usually on the first day of life.

Diagnosis is based on antigenic and functional plasma assays of protein C.

Treatment of Protein C Deficiency

  • Anticoagulation

Patients with symptomatic thrombosis require anticoagulation with heparin or low molecular weight heparin, followed by warfarin. Use of the vitamin K antagonist, warfarin, as initial therapy occasionally causes thrombotic skin infarction by lowering vitamin K–dependent protein C levels before a therapeutic decrease has occurred in vitamin K–dependent coagulation factors.

It is probable, but not yet certain, that the direct oral anticoagulant (DOAC) inhibitors Treatment In healthy people, homeostatic balance exists between procoagulant (clotting) forces and anticoagulant and fibrinolytic forces. Numerous genetic, acquired, and environmental factors can tip... read more of either thrombin (dabigatran) or factor Xa (eg, rivaroxaban, apixaban) can be used in place of other anticoagulants for this disorder.

Neonatal purpura fulminans is fatal without replacement of protein C (using normal plasma or purified concentrate), along with anticoagulation with heparin or low molecular weight heparin.

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Overview of Thrombotic Disorders
Thrombotic disorders can be caused by genetic defects, which increase the risk of venous thromboembolism, or acquired defects, which increase the risk of arterial and venous thrombosis. Of the acquired causes, which of the following is most likely to increase a patient’s risk of venous thrombosis?
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