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Protein C Activity
Test Code1777X
CPT Codes
85303
Preferred Specimen
1 mL frozen plasma collected in 3.2% sodium citrate (light blue-top) tube
Minimum Volume
0.5 mL
Instructions
Platelet-poor plasma: Centrifuge light blue-top tube for 15 minutes at approximately 1500 g within 60 minutes of collection. Using a plastic pipette, remove plasma, taking care to avoid the WBC/platelet buffy layer and place into a plastic vial. Centrifuge a second time and transfer platelet poor plasma into a new plastic vial. Plasma must be free of platelets (<10,000/mcL). Freeze immediately and ship on dry ice.
Specimen Stability
Frozen -20° C: 14 days
Frozen -70° C: 1 year
Frozen -70° C: 1 year
Reject Criteria (Eg, hemolysis? Lipemia? Thaw/Other?)
Hemolysis • Received thawed • Received room temperature • Received refrigerated
Methodology
Clotting Assay
Setup Schedule
Set up: Sun-Fri; Report available: 2-3 days
Limitations
Expected impact by therapeutic levels (potential interference depends upon drug concentration): Warfarin: decrease; Heparin (UFH or LMWH): UFH-no effect, LMWH-may falsely increase at higher levels; Dabigatran or Argatroban (Thrombin Inhibitors): may falsely increase; Rivaroxaban or Apixaban (Factor Xa Inhibitors): may falsely increase.
Clinical Significance
Aids in diagnosis of decreased activity of Protein C characterized by recurrent venous thrombosis. Acquired deficiencies associated with Protein C include: Oral anticoagulant therapy, liver disease, vitamin K deficiency, malignancy, consumptive DIC, surgery, trauma, antibodies to Protein C and hepatic immaturity of the newborn.
