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.
75 - 125%
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.
- Antithrombin III Assay, Functional
- Serine Protease Inhibitor
- ANTITHROMBIN III ACTIVITY
- Factor 10a Inhibition
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.
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.