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

 Lt blue Sodium citrate (Na Cit) - 2.7mL

• 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.

• Platelet poor citrated plasma samples (PPP) should be obtained by double centrifugation.

  1. Centrifuge for 10 minutes and carefully remove 2/3 of the plasma using a plastic transfer pipette, being careful not to disturb the cells.
  2. Deliver to a plastic transport tube, cap, and recentrifuge for 10 minutes.
  3. Use a second plastic pipette to remove the plasma, staying clear of the platelets at the bottom of the tube.
  4. Transfer the plasma into a LabCorp frozen purple tube with screw cap, labelled as PPP
  5. Freeze immediately and maintain frozen until tested.

Screw-cap polypropylene frozen transport vial/tube - 4mL (LabCorp)

Frozen - 28 days

Freeze/thaw cycles - stable x3

• 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%