Thrombophilia: How To Test? How To Manage?

By Julie Hambleton, MD

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Protein C and S

PC and PS are vitamin K-dependent glycoproteins that are involved in the inactivation of activated factors V and VIII. PC is slowly activated to activated protein C (APC) by thrombin. PS, in and of itself, has no intrinsic anticoagulant activity. Instead, it enhances the affinity of APC for negatively charged phospholipids, such as those found on the platelet surface, forming a membrane-bound APC-PS complex that renders factors Va and VIIIa more easily accessible to APC-mediated cleavage.

Deficiencies in PC and PS are transmitted as autosomal-dominant traits. Homozygous PC deficiency is associated with neonatal purpura fulminans and warfarin-induced skin necrosis. The frequency of symptomatic PC and PS deficiencies is somewhat greater than that of AT deficiency, but it is still uncommon, being 2.2 to 3.2% in unselected patients with venous thrombosis (first unprovoked DVT) and 3 to 3.8% in selected patients (recurrent VTE with or without family history of VTE).

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