Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (1178 page)

   Nephrotic syndrome

   Ischemic heart disease

   Pregnancy

   Oral contraceptives

   Heparin therapy

   Increased age

Decreased In

   Congenital heterozygous deficiency of protein C, which is an autosomal trait with variable penetrance, with a prevalence of 1/500 individuals of European descent. Homozygous deficiency results in life-threatening massive thromboses in neonates (purpura fulminans).

   Acquired: liver disease, vitamin K deficiency or use of vitamin K antagonists,
L
-asparaginase therapy, DIC, acute-phase reaction (thrombotic, inflammatory, surgical).

   Limitations

   Highly elevated factor VIII levels falsely lower protein C measurements

   Lupus anticoagulant may falsely elevate reported protein C levels

PROTEIN S
*

   Definition

   Protein S is a plasma protein synthesized in the liver and dependent on vitamin K for its functionality. It has an anticoagulant function, serving as a cofactor for activated protein C. Together they inhibit the activities of activated factors V and VIII. Protein S circulates in a free form,
free protein S
(about 40% of the protein), where the major cofactor function resides, and as bound to complement C4b,
bound protein S
. The bound form may also play a role in the natural anticoagulation mechanism, this possibility being under active investigation.