| Description: |
Protein C is a natural anticoagulant produced in the liver. It is vitamin K dependent and requires thrombin and thrombomodulin for activation. Activated protein C in the presence of cofactor protein S inactivates factors Va and VIIIa, thereby limiting coagulation. Patients heterozygous for deficiency of protein C or S may exhibit recurrent venous thrombosis at a young age (peak incidence between ages 15 and 40). Heterozygotes also appear to have an increased risk of coumadin-induced skin necrosis. Patients homozygous for protein C deficiency present with generalized microvascular thrombosis in the neonatal period (purpura fulminanas). Normal neonates have lower levels of protein C than adults. Warfarin therapy will result in low protein C levels. See also Thrombosis screen and Activated Protein C Resistance in the Test Directory at www.stanfordlab.com.
Protein S is a vitamin K-dependent co-factor for activated protein C, which serves to inactivate factors Va and VIIIa. Protein S deficiency is clinically indistinguishable from protein C deficiency, with heterozygous individuals at an increased risk of recurrent venous thrombosis. The assay is useful for evaluation of thrombophilic patients, in particular those who have a family history of thrombosis, thrombosis at a young age (<40 years), recurrent thrombosis or thrombosis at unusual sites (inferior vena cava, mesenteric veins). Normal neonates have lower protein S levels than adults do. Pregnancy normally results in decreased protein S levels. Patients with the factor V Leiden mutation may have artificially low functional Protein S levels. Protein S is a vitamin K-dependent protein, so warfarin use will result in low levels. |
