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Antithrombin III Activity with Reflex to Antithrombin III Antigen
Test Code8267
CPT Codes
85300
Includes
If Antithrombin III Activity is below reference interval, then Antithrombin III Antigen will be performed at an additional charge (CPT code(s): 85301).
Preferred Specimen
1 mL frozen platelet-poor plasma (x2) collected in 3.2% sodium citrate (light blue-top) tubes
Minimum Volume
0.5 mL (x2)
Instructions
Please submit a separate, frozen vial for each special coagulation assay ordered.
Draw blood in a light blue-top tube containing 3.2% sodium citrate, mix gently by inverting 3-4 times. Centrifuge 15 minutes at 1500 g within one hour 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(s). Freeze immediately and transport on dry ice.
Draw blood in a light blue-top tube containing 3.2% sodium citrate, mix gently by inverting 3-4 times. Centrifuge 15 minutes at 1500 g within one hour 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(s). Freeze immediately and transport on dry ice.
Transport Container
Plastic vials
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?)
Gross hemolysis • Grossly lipemic • Grossly icteric
Methodology
Chromogenic Substrate
Setup Schedule
Set up: Mon-Fri; Report available: 1-4 days
Limitations
Falsely elevated results may be caused by heparin cofactor II.
Reference Range
Antithrombin III Activity
1 day-1 month | 41-108 % normal |
31 days-2 months | 50-120 % normal |
3-5 months | 73-120 % normal |
≥6 months | 80-135 % normal |
Clinical Significance
Aids in characterization of Antithrombin deficiency (AT, previously referred to as Antithrombin III) which is associated with increased thrombotic risk. Type I deficiency is characterized by reduction in activity and antigen levels simultaneously. With type II deficiency, activity levels are lower in comparison to the antigen levels (dysfunctional protein). Acquired deficiency, more common than inherited defects, can occur due to: liver disease, nephrotic syndrome, heparin therapy, disseminated intra- vascular coagulation (DIC), sepsis, and L-asparaginase chemotherapy.
Anticoagulant Interference: 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 activity levels; Rivaroxaban, Apixaban, Edoxaban (Factor Xa Inhibitors): no effect.
Anticoagulant Interference: 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 activity levels; Rivaroxaban, Apixaban, Edoxaban (Factor Xa Inhibitors): no effect.