Antithrombin III, Immunologic, Plasma
AT III Antigen/Immunologic
Assessing abnormal results of the antithrombin activity assay (ATTF / Antithrombin Activity, Plasma), which is recommended as the primary (screening) antithrombin assay
Diagnosing antithrombin deficiency, acquired or congenital, in conjunction with measurement of antithrombin activity
An adjunct in the diagnosis and management of carbohydrate-deficient glycoprotein syndromes
If patient is being treated with heparin, this should be noted as heparin treatment may lower plasma antithrombin.
1. Centrifuge, remove plasma, and centrifuge plasma again.
2. Freeze plasma immediately (no longer than 4 hours after collection) at -20 degrees C or, ideally, < or =-40 degrees C.
1. Double-centrifuged specimen is critical for accurate results as platelet contamination may cause spurious results.
2. Each coagulation assay requested should have its own vial.
Antithrombin antigen results are potentially affected by:
-Heparin (unfractionated or low-molecular-weight) >4 U/mL
-Hemoglobin >7 g/L
-Bilirubin >500 mg/L
-Lipemia; may lead to an over-estimation of the antithrombin antigen level
-Rheumatoid factor (RF) >800 IU/mL; may lead to overestimation of the antithrombin antigen level
-Anti-rabbit antibodies in certain subjects leads to aberrant results
-Heparin therapy may temporarily decrease plasma antithrombin antigen into the abnormal range
Hereditary antithrombin deficiency is much less common than acquired deficiency. Diagnosis of hereditary deficiency requires clinical correlation, testing of both antithrombin activity and antithrombin antigen, and may be aided by repeated testing and by family studies. DNA-based diagnostic testing may be helpful, but is generally not readily available.
Acquired antithrombin deficiency may occur in association with a number of conditions (see Clinical Information). The clinical significance (thrombotic risk) of acquired antithrombin deficiency is not well established, but accumulating information suggests possible benefit of antithrombin replacement therapy in carefully selected situations.(4)
Increased antithrombin activity has no definite clinical significance.