Protein S, Functional
Protein S, Functional-994
Protein S Activity
Confirmation and characterization of protein S (PS) congenital deficiency
The presence of heparin or lupus anticoagulants leads to overestimation of PS. Activated Protein C (aPC) resistance due to Factor V Leiden mutation or some other cause can falsely lower measured PS activity levels
Avoid Warfarin (Coumadin) therapy for two weeks and heparin therapy for two days prior to testing
- Evacuated collection tubes must be filled to completion to ensure a proper blood to anticoagulant ratio.
- Immediately following collection, mix sample thoroughly by gently inverting 8 - 10 times to prevent clotting
- A discard tube is not required prior to collection of coagulation samples, except when using a winged blood collection device (ie, "butterfly"), in which case a discard tube should be used.
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Platelet poor citrated plasma samples (PPP) should be obtained by double centrifugation.
- Centrifuge for 10 minutes and carefully remove 2/3 of the plasma using a plastic transfer pipette, being careful not to disturb the cells.
- Deliver to a plastic transport tube, cap, and recentrifuge for 10 minutes.
- Use a second plastic pipette to remove the plasma, staying clear of the platelets at the bottom of the tube.
- Transfer the plasma into a LabCorp frozen purple tube with screw cap, labelled as PPP
- Freeze immediately and maintain frozen until tested.
Frozen (strict)
- Gross hemolysis
- Clotted specimen
- Frozen specimen thawed in transit
- Improper labeling (unlabeled or mislabeled)
The patient plasma is added to PS-depleted normal plasma with normal levels of all factors but PS. The mixture is supplemented with excess aPC and factor V is then added. The extent of prolongation of the time to clot formation after calcium chloride is added is proportional to plasma PS activity.
63-140%