Antithrombin III Activity and Antigen

Test Code

7017

CPT Codes
85300, 85301

Includes

Antithrombin III Activity
Antithrombin III Antigen

Preferred Specimen

1 mL frozen platelet-poor plasma (x2) collected in separate 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.

Transport Container

Plastic vial

Transport Temperature

Frozen

Specimen Stability

Room temperature: Unacceptable
Refrigerated: Unacceptable
Frozen: 30 days

Methodology
Chromogenic Substrate • Immunoturbidimetric

Setup Schedule

Monday-Friday Evening
Report available: Next Day

Limitations

Antithrombin III Activity: 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.
Antithrombin III Antigen: 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): no effect; Rivaroxaban or Apixaban (Factor Xa Inhibitors): no effect.

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

Antithrombin III Antigen

80-120 % 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 intravascular 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.

The CPT Codes provided in this document are based on AMA guidelines and are for informational purposes only. CPT coding is the sole responsibility of the billing party. Please direct any questions regarding coding to the payor being billed. Any Profile/panel component may be ordered separately. Reflex tests are performed at an additional charge.