Protein C Antigen, Sodium Citrate Whole Blood

Protein C test along with protein S, helps to investigate for any hypercoagulable disorder in which there is excess clotting. Protein C and protein S tests also help to diagnose the cause of inappropriate thrombus (blood clot) formation such as deep venous thrombosis (DVT) or a venous thromboembolism. Protein C and protein S are vitamin K-dependent anticoagulants synthesized by the liver. Protein C circulates in the blood (plasma) and protein S is present in the platelets. The half-life of protein C is 6 to 10 hours. Thrombin in the presence of thrombomodulin (endothelial cell cofactor) activates protein C and protein S. These activated forms act as anticoagulant by inactivating the active forms of coagulation factors like factor V and factor VIII. Protein C also enhances fibrinolysis by inactivating plasminogen activator inhibitor (PAI-1). The activity of activated protein C is enhanced by protein S. Protein S also has a direct Activated Protein C independent anticoagulant activity. Deficiency of protein C and protein S results in thrombotic events (mostly venous thromboemboli; arterial thrombosis results in stroke, myocardial infarction etc). However at times it could be asymptomatic. Hereditary heterozygous protein C deficiency is of two types: Type I, associated with decreased protein C antigen and activity and type II which is associated with decreased protein C function and normal antigen levels. There are 3 types of protein S deficiencies, according to the levels of total and free protein S antigen and protein S activity. Types I and III protein S deficiency are more common than type II protein S deficiency. Vitamin K deficiency, oral anticoagulants, liver diseases etc are associated with acquired form of protein C and protein S deficiencies. Protein C functional activity assay is advised when suspecting congenital protein C deficiency. Based on the results of protein C activity - protein C antigen, protein S tests may be needed, to classify and determine the severity of disorder. It is advised to look for acquired causes of protein C deficiency, such as Vitamin K deficiency, oral anticoagulants, liver diseases etc.

1. Can protein C and protein S test be done when the patient is on anticoagulant therapy?

Anticoagulant drugs may alter protein C and protein S levels and/ or interfere with the activity assays. Hence it is advised to stop the treatment for a limited period of time, before the test is done.

2. Can protein C and protein S levels be increased?

If the deficiency of protein C and/ or protein S levels is temporary as in pregnancy and infection, the levels return to normal by themselves. Protein C or protein S deficiency due to liver diseases or vitamin K deficiency are treated by addressing the underlying condition. In inherited cases lowering other clotting risk factors (like smoking, oral contraceptive intake etc.) is advised.

3. Should relatives of patients with inherited protein C or protein S deficiency also be tested?

Not required, as the penetrance of genes is low. However it is done if there is a strong family history or a history of developing early age thrombosis.