Protein S, Activity

Protein S, Functional

7 days

Clotting time

Males: 77-143% Females: 55-123%

Double-centrifuged specimen is critical for accurate results as platelet contamination may cause spurious results. Rejection criteria: Gross hemolysis; incorrect blood to anticoagulant ratio, improper labelling; clotted specimen; specimen diluted with IV fluids; samples thawed in transit; incorrect sample type; sample out of stability. Do not draw from an arm with a heparin lock or heparinized catheter.

Accredited NRL Laboratory

Once a week

Protein S functions as a cofactor for activated Protein C, contributing to the regulation of coagulation through inactivation of factors Va and VIIIa. Functional Protein S testing is indicated in the workup of venous thromboembolism, hereditary thrombophilia, recurrent pregnancy loss, and neonatal purpura fulminans.

Platelet-poor plasma

1 aliquot containing minimum 1ml of plasma

Sodium citrate (light blue top), filled to the line

Ideally, the patient should not be on anticoagulation therapy. Avoid heparin, direct Xa, and thrombin inhibitor therapies for about three days prior to testing. Indicate and provide details if patient is on anticoagulant.

Plasma should be platelet free as possible. Platelet count should be less than 10 x 109/L. Double centrifugation:
Perform centrifugation for 15 mins at 2000-2500 g. Carefully remove 2/3 of plasma using a transfer pipette without disturbing the interface layer between plasma and cells. Transfer plasma to an plastic aliquot tube and repeat the centrifugation step. Using a second pipette, separate plasma again into another plastic aliquot tube, staying clear of the platelet layer at the bottom of the tube. Centrifuge, separate and freeze sample ideally within 1 hour of collection time but no more than 2 hours. Specimens must be completely frozen prior to transport and must be received in a frozen condition.