Merck Manual

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Protein Z 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 protein Z helps inactivate coagulation factor Xa, deficiency or dysfunction of protein Z predisposes to venous thrombosis (mainly in patients who also have other clotting abnormalities).

Protein Z, a vitamin K–dependent protein, functions as a cofactor to down-regulate coagulation by forming a complex with the plasma protein, Z-dependent protease inhibitor (ZPI). The complex predominantly inactivates factor Xa on phospholipid surfaces.

The consequence of protein Z or ZPI congenital deficiency, or of acquired autoantibodies to protein Z, in the pathophysiology of thrombosis, fetal loss, and cancer (ovarian or gastric) is not completely clear; however, a defect of either protein Z or ZPI may make thrombosis more likely if an affected patient also has another congenital coagulation abnormality (eg, factor V Leiden) or an acquired autoantibody against a phospholipid-bound protein (an antiphospholipid antibody).

Quantification of protein Z, ZPI, and protein Z autoantibodies is done in specialized regional laboratories by plasma electrophoresis, immunoblotting, and enzyme-linked immunosorbent assay.

It is not yet known whether anticoagulant therapy or prophylaxis is indicated in protein Z or ZPI deficiency.

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