Protein S Activity, Clot

Protein S activity is a clot-based quantitative assay to measure the functional protein S level for diagnosis of congenital or acquired protein S deficiency. Protein S activity is recommended if initial testing with Free Protein S Antigen (PSAGF) is decreased. Congenital protein S deficiency is characterized by recurrent thrombosis and the classification of the protein S deficiency is dependent upon the protein S antigen and activity levels. Protein S is a vitamin K-dependent protein. Patients on warfarin therapy may see a decrease in protein S activity due to the vitamin K antagonistic effect of the drug. Protein S activity may also be decreased in the setting of acute phase responses, pregnancy, cirrhosis, L-asparaginase treatment, use of oral contraceptives, DIC or acute thrombotic event.

Recommend Free Protein S Antigen (PSAGF) assay if the patient is taking direct oral anticoagulants.

Outside clients should fill and submit Coagulation Patient Clinical History Form: Coagulation Patient Clinical History Form

**Laboratory Medicine resident's approval is required for hospital inpatients and patients in Emergency Department.**

Approval is NOT required for hospital outpatients, clinic patients or outside clients. Note: If request simply states PROTEIN S, see PSAGF

UW-MT Instructions: Take specimen to UW-MT Coag lab for processing. Coag tech will freeze plasma sample for transport to HMC Coag.

HMC Instructions: Take specimen to HMC Coag lab for processing.

Outside Laboratory: Centrifuge for 10 minutes, remove plasma & re-spin plasma for another 10 minutes. Decant & Freeze plasma (minimum 1.0 mL) @ -20°C to -80°C. Send frozen on dry ice.