Antithrombin III Activity with Reflex to Antithrombin III Antigen

Message

Platelet poor plasma: Centrifuge light blue-top tube 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). Do not thaw. Freeze immediately and ship on
dry-ice.

Test Code

AT3AR

Alias/See Also

LAB10064

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

2 mL frozen plasma

Minimum Volume

1 mL

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 vials

Transport Temperature

Frozen

Specimen Stability

Room Temperature: Unacceptable Refrigerated: Unacceptable
Frozen: 21 days

Reject Criteria (Eg, hemolysis? Lipemia? Thaw/Other?)

3.8% Sodium citrate (light blue-top) tube

Methodology

Chromogenic Substrate

Setup Schedule

Mon-Fri evening

Report Available

Next day

Limitations

Falsely elevated results may be caused by heparin cofactor II.

Reference Range

Antithrombin III Activity 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 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.

Performing Laboratory
Quest Diagnostics Nichols Institute 14225 Newbrook Drive Chantilly, VA 20153

Last Updated: February 17, 2023

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.