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Antithrombin III Activity
Test Code216
CPT Codes
85300
Preferred Specimen
1 mL frozen platelet-poor plasma collected in 3.2% sodium citrate (light blue-top) tube
Minimum Volume
0.5 mL
Instructions
Centrifuge light blue-top tube 15 minutes at approx. 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.
Transport Temperature
Frozen
Specimen Stability
Room temperature: Unacceptable
Refrigerated: Unacceptable
Frozen: 30 days
Refrigerated: Unacceptable
Frozen: 30 days
Reject Criteria (Eg, hemolysis? Lipemia? Thaw/Other?)
Hemolysis • Thawed plasma
Methodology
Chromogenic Substrate
Setup Schedule
Set up: Tues-Sat; Report available: 1-3 days
Limitations
Expected impact by therapeutic levels (potential interference depends upon drug concentration): Warfarin: no effect; Heparin (UFH or LMWH): no effect to decrease (UFH may decrease levels physiologically but no assay interference); Dabigatran or Argatroban (Thrombin Inhibitors): may falsely increase; Rivaroxaban or Apixaban (Factor Xa Inhibitors): no effect.
Clinical Significance
Aids in the detection of hypercoagulable states associated with venous thrombotic episodes. May be useful in patients who appear to be hyporesponsive to heparin.
