This algorithm is intended for use with additional UpToDate content on protein C deficiency.
VTE: venous thromboembolism; DIC: disseminated intravascular coagulation; VKA: vitamin K antagonist. * In general, in the absence of conditions that interfere with the protein C assays, a normal protein C is >65 to 70%. The absolute threshold for deficiency is unclear. In most cases, protein C <55% is likely deficient, whereas levels from 55 to 65% are indeterminate. Interpretation of a specific abnormal result should be based upon the reference range reported by the laboratory. ¶ Obtain hematology consultation to assist in interpretation of abnormal test results and to guide further evaluation. Δ Warfarin (or another VKA) reduces functional protein C and, to a lesser extent, protein C antigen levels. Other anticoagulants, such as heparin, direct thrombin inhibitors, direct oral factor Xa inhibitors, and fondaparinux, do not affect circulating protein C levels. However, these agents may interfere in selected functional assays for protein C activity (eg, those with clotting endpoints).
