Laboratory Services

Antithrombin Activity, Plasma

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Updated Test Information:

Test Description
Antithrombin Activity, Plasma

Antithrombin Activity; AT3 Activity/Functional; AT III Activity/Functional; Anti-Thrombin III

Test ID
General Information

Useful for:

  • Diagnosis of antithrombin deficiency, acquired or congenital

  • Monitoring treatment of antithrombin deficiency disorders, including infusion of antithrombin therapeutic concentrate

Specimen Type


Specimen Requirements

Light-blue top (3.2% sodium citrate)

Additional Processing Details

  • For complete instructions, see Coagulation Guidelines for Specimen Handling and Processing

  • Centrifuge, transfer all plasma into a plastic vial, and centrifuge plasma again

  • Aliquot plasma into a plastic vial leaving 0.25 mL in the bottom of centrifuged vial

  • Freeze plasma immediately (no longer than 4 hours after collection) at (-20) degrees C or, ideally ≤ (-40) degrees C.


Frozen: 14 days

Unacceptable Specimen Conditions

  • Gross hemolysis

  • Gross lipemia

  • Gross icterus


Antithrombin functional result is affected by:

  • Heparin (unfractionated or low-molecular-weight) >4 U/mL

  • Alpha-1-antitrypsin >4 mg/mL

  • Alpha-2-macroglobulin >10 mg/mL

  • Heparin cofactor II >4 U/mL

  • Hemoglobin >500 mg/dL

  • Bilirubin >40 mg/dL

  • Triglycerides >2300 mg/dL

  • Heparin therapy may temporarily decrease plasma antithrombin activity into the abnormal range

  • Antithrombin activity in serum specimens may be significantly lower than in plasma


Chromogenic Assay

Estimated TAT

1 - 3 days

Testing Schedule

Monday - Saturday


7 days

CPT Code(s)


Additional Information
Minimum Sample Volume

0.5 mL

Reference Range
  • Normal values (%): 80 - 130
  • Normal, full-term newborn infants have lower levels (≥ 35-40%) that reach normal values by age 90 days
  • Premature infants (30-36 weeks gestation) have lower levels that reach normal values by age 180 days.


Performing Lab


LOINC Code(s)