Activated protein C resistance is a hemostatic disorder characterized by a poor anticoagulant response to activated protein C (APC). This results in an increased risk of venous thrombosis. An anticoagulant is a substance that prevents coagulation; that is, it stops blood from clotting. ... Protein C is a major physiological anticoagulant. ... A venous thrombosis is a blood clot that forms within a vein. ...
Activated protein C (with protein S as a cofactor) degrades Factor Va and Factor VIIIa. Activated protein C resistance is the inability of protein C to cleave factors V and/or VIII. This may be hereditary or acquired. The best known and most common hereditary form is Factor V Leiden. Acquired forms occur in the presence of elevated Factor VIII concentrations. Factor V is a protein of the coagulation system, rarely referred to as proaccelerin or labile factor. ... <<a href=b class=external free title=b>b>Factor VIII</<a href=b class=external free title=b>b> (FVIII) is an essential [clot]ting factor. ... Factor V Leiden (sometimes Factor VLeiden) is a hypercoagulability disorder in which Factor V, one of the coagulation factors, cannot be deactivated. ...
In most cases, APC resistance is associated with a single missense mutation in the gene for coagulation factor V (FV (Leiden)). It has been estimated that up to 64% of patients with venous thromboembolism might have activated protein C resistance.
References
Nicolaes GA, Dahlback B (2003). Congenital and acquired activated protein C resistance. Semin Vasc Med3 (1): 33-46. PMID 15199491
Dahlback B (2003). The discovery of activated protein C resistance. J Thromb Haemost1 (1): 3-9. PMID 12871530
Sheppard DR (2000). Activated protein C resistance: the most common risk factor for venous thromboembolism. J Am Board Fam Pract13 (2): 111-5. PMID 10764192
ProteinC deficiency is a rare genetic disorder that predisposes to venous thrombosis and habitual abortion.
In initial stages of action, inhibition of proteinC may be stronger than inhibition of the vitamin K-dependant coagulation factors (II, VII, IX and X), leading to paradoxical activation of coagulation and necrosis of skin areas.
Drotrecogin alpha (activated) is recombinant activatedproteinC. It is used in the treatment of sepsis and disseminated intravascular coagulation.
The activatedproteinC (APC) resistance test is a recently described clotting assay that is an important new diagnostic tool to define a cause of hypercoagulability in patients with thrombosis.
ProteinC, in the presence of its cofactor thrombomodulin and thrombin, is enzymatically cleaved to its active form, ActivatedProteinC. APC is an important natural anticoagulant which functions by inactivating the critical coagulation factors FVa and FVIIIa.
The activatedproteinC (APC) resistance test may aid in defining a cause of hypercoagulability in up to 25% of patients with thrombosis and has identified a new congenital cause of thrombosis due to an abnormal factor V molecule.
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