Test Overview
Test Methodology

Chromogenic

Test Usage

AT3 levels are used as a possible indicator of hypercoagulability, and to test for the hereditary deficiency of antithrombin. AT3 levels might also be of use in cases of suspected heparin failure especially prior to heparinization.

Reference Range *

75 - 125%

Test Limitations

If a patient is on heparin therapy or has received heparin within the last 10 days, the results of this test may be falsely decreased. The AT3 level may be diminished for several days after surgery or a thrombotic event. Warfarin therapy has been reported to raise AT3 levels.

Test Details
Days Set Up
Tuesday
Analytic Time

1 hour

Soft Order Code
AT3
MiChart Code
Antithrombin III
Synonyms
  • Antithrombin III Assay, Functional
  • Serine Protease Inhibitor
  • AT3
  • ANTITHROMBIN III ACTIVITY
  • Factor 10a Inhibition
Laboratory
Hematopathology
Section
Coagulation
Specimen Requirements
Collection Instructions

Collect specimen in a blue top (citrate 3.2%) tube. Mix by inversion. Specimen should arrive at lab within 3 hours of collection; transport at room temperature. Alternatively, centrifuge, aliquot plasma into a plastic vial, and freeze the specimen within 4 hours of collection. Transport frozen specimen on dry ice. Collection of the blood through lines that have been previously flushed with heparin should be avoided. If the blood must be drawn through a VAD (vascular access device), the line should be flushed with 5 mL of saline and the first 5 mL of blood or six dead space volumes of the VAD discarded.

Rejection Criteria
Specimens will be rejected if not properly filled, clotted, grossly hemolyzed, or contaminated with heparin
Contraindications
Test is not indicated for patients on heparin, low-molecular-weight heparin, or direct thrombin inhibitor therapy. This test is not indicated for inpatient evaluation of acute thrombosis.
Blue Top Tube
Normal Volume
Full 2.7mL tube or 1 mL plasma aliquot
Minimum Volume
Full 1.8mL tube or 1 mL plasma aliquot
Storage Temperature
Room temperature for whole blood or frozen aliquot of citrated plasma.
Additional Information

Individuals with hereditary AT3 deficiency will show resistance to anticoagulation with heparin but can be anticoagulated with warfarin. Decreased AT3 levels may be found in women taking oral contraceptives, in conditions associated with \"consumption\" of coagulation proteins (pulmonary embolism, thrombophlebitis, acute myocardial infarction, and DIC), and in liver disease.

Billing
CPT Code
85300
Fee Code
31115