Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (1177 page)

   After exercise

   Limitations

   Highly alkaline urine produces false-negative results.

   Not reliable to quantify urinary immunoglobulin light chains.

PROTEIN C
*

   Definition

   Protein C is a vitamin K–dependent coagulation inhibitor which, in its activated form, activated protein C (APC), down-regulates the activity of factors V and VIII through proteolysis. It is produced mainly in the liver. Congenital deficiency leads to a high incidence of venous thrombosis. Because of its short half-life, measured in hours, initiation of vitamin K antagonist therapy results in very rapid decline in the protein C level in normal individuals. In heterozygous individuals, such therapy may lead to very low levels of protein C activity—approaching 0%, with a high risk for venous thrombosis and coumarin necrosis.

   
Normal range:
70–140%.

   Use

   Protein C functional level is examined in cases of suspected congenital thrombophilia, such as suspected in patients with unprovoked venous thromboembolism, especially when in unusual sites.

   Determination of protein C antigen discriminates between type 1 protein C deficiency (concordant decrease of functional and immunologic assays) and type II deficiency, where the antigen level is normal. This difference has no known clinical implication.

   Protein C should not be assayed in patients taking vitamin K antagonists.

   Interpretation

Increased In

   Diabetes