Complete absence has led to fatal thrombosis in neonates. Elevated levels of protein C may be seen in patients with diabetes, nephrotic syndrome, pregnancy, and oral contraceptive use. Patients on oral anticoagulants will have decreased functional protein C values. Patients should be off oral anticoagulant therapy for at least two weeks for accurate measurement of functional protein C levels. Artifactually elevated levels of functional protein C may be seen in patients with intrinsic pathway inhibitors, lupus anticoagulants, and in patients receiving heparin therapy.
Reference intervals listed are for normal adults.
Bertina RM, et al. The use of functional and immunologic assay for plasma protein C in the study of the heterogenicity of congenital protein C deficiency. C assay using Protac, a novel protein C activator.