Protein S Activity (PS)
Department: Coagulation
Test Synonym(s): LAB491, PS, PS Act
CPT Codes: 85306
Methodology: Clotting
Reference Range: 55 - 123%
Tube Type: One 2.7mL Light blue top - 3.2% Sodium Citrate
Specimen: Citrated platelet poor plasma - Requires double centrifugation if sending a plasma aliquot. Aliquot(s) must be frozen if not received by lab within 4 hours of collection.
Alternate Specimen: None
Pediatric Requirements: Pediatric: One 2.7mL Light blue top - 3.2% Sodium Citrate. Neonatal: One 1.8mL Light blue top - 3.2% Sodium Citrate.
Volume: 1.0 mL plasma
Minimum Volume: 1.0 mL plasma
Temperature: Room Temperature for Light blue top tube, must be received within 4 hours of draw. Plasma aliquot(s) must be frozen if not received by lab within 4 hours of collection.
Stability: Room temperature: 4 hours, Frozen: -70 C for one month
Reasons for Rejection: Clotted sample, incorrectly filled tubes, incorrect tube type, grossly hemolyzed sample, grossly lipemic sample, grossly icteric sample, whole blood >4.0 hours old
Days Performed: Monday - Friday
Times Performed: Twice weekly
TAT: 1-4 days
Significance: Therapeutic warfarin results in a decreased level of Protein S. Presence of a Lupus anticoagulant or anti phospholipid antibodies in the plasma may interfere with this assay. In this circumstance, measuring free Protein S antigen levels may be more useful. Direct Thrombin and both Direct and Indirect anti-Xa interferes with the assay producing spurious results.
Special Instructions: Protein S Activity is reduced during pregnancy and inflammation. Performed twice weekly. Collect partial waste tube if using butterfly device. Do not send on ice. Deliver to lab immediately.
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