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Antithrombin III (atIII) reagent assay

Product Method Size Catalog Price Quantity
Antithrombin III (atIII) reagent assay Coagulation R1 R1 4 x 2ml, R2 4 x 2ml ANT2754 $826.25
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  • Format
  • Working Stability 15-25 °C
    2 days
  • Working Stability 2-8 °C
    14 days
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Intended Use

For the quantitative in vitro determination of Antithrombin III (AT III) in human plasma by chromogenic method. This product is suitable for use with manual or semi-automated methods.

Clinical Significance

Antithrombin III is an inhibitor of plasma serine proteases. An important function of Antithrombin III is the inhibition of thrombin activity. Normally the rate of thrombin inhibition by Antithrombin III is slow (progressive Antithrombin activity), however, the rate of inhibition can be enhanced several thousand-fold in the presence of Heparin (Heparin cofactor activity).

Tolefsen and Blank reported another rapid heparin-dependent thrombin inhibitor, Heparin Cofactor II, in human plasma. This protein can interfere with Antithrombin III determinations especially at high Heparin concentrations (2 USP units/ml).

Antithrombin testing is primarily ordered, along with other tests for hypercoagulable disorders, to investigate the cause of recurrent venous thrombosis and evaluate how patients are responding to heparin.

Lower than normal ATIII may be due to:

  • Deep vein thrombosis, inflammation of the veins or pulmonary embolus
  • Liver dysfunction (coagulopathy)
  • Sepsis, premature birth
  • Kidney disease
  • Nephrotic syndrome
  • Bone marrow transplant
  • An inherited condition causing lower blood clotting protein levels

Higher than normal ATIII levels are associated with the use of anabolic steroids.


In this two-stage method Thrombin is added to a plasma dilution containing Antithrombin III in the presence of excess Heparin. After an initial incubation period (stage 1) residual thrombin activity is determined with a thrombin-specific chromogenic substrate (stage 2). The residual thrombin activity is inversely proportional to the Antithrombin III concentration.

In order to confer specificity to Antithrombin III, this present assay system uses a lower final Heparin concentration where heparin-enhanced inactivation of thrombin by Heparin Cofactor II is negligible. In addition, human Heparin Cofactor II reacts more readily with human thrombin than with bovine thrombin. Thus further specificity for Antithrombin III is imparted in the present assay system by the use of bovine thrombin.

Available Applications

  • Manual