Antithrombin (AT)


Antithrombin (AT) is a progressive inhibitor of thrombin (factor IIa) but also of other serine proteases, such as factor Xa, factor IXa, XIa and XIIa, plasmin and kallikrein. Heparin accelerates dramatically the inhibition of factor IIa and Xa1. Antithrombin concentration, like protein C and protein S concentrations, plays an important role in the hemostatic balance. Antithrombin is a single chain glycoprotein synthesized in the liver2.

By definition, the 100 % Antithrombin concentration corresponds to the concentration in a normal human citrated plasma pool, obtained by pooling plasmas from healthy males or females aged from 18 to 55 years, and out of any medication. Normal range expected about 75% up to about 125%, to be verified and validated in the exact laboratory working conditions (instrument and application, lot, calibrator used…). Antithrombin concentration ≤ 70% indicates the presence of a deficiency, which must be confirmed by another test and/or by testing another plasma sample from the patient. The Antithrombin concentration is decreased during pregnancy and during oral contraceptive therapy.

Spontaneous thromboembolic diseases are observed in presence of congenital deficiencies. These congenital deficiencies are classed in 4 different groups:

Type Description
Type I: Decreased Antithrombin concentration and decreased Antithrombin activity; this is the most frequent case.
Type II:  
 Reactive Site (RS) Normal Antithrombin concentration and decreased biological activity; a protein abnormality is present at the active site.
Heparin Binding Sites (HBS)  Normal Antithrombin concentration, normal Antithrombin activity in the absence of heparin, but decreased in its presence.
Pleiotropic Decreased Antithrombin concentration and activity; non functional protein and at a lowered level. 

Overview Assays

Product Name Assay principle Reference Package
BIOPHEN AT anti-(h)-Xa LRT (CE-IVD)  Chromogenic assay for the in vitro quantitative determination of Antithrombin (AT) activity  using an anti Xa method. Reagents are in the liquid presentation, ready to use. Makes use of Human Factor Xa. 221123


 2 x 3 x 3 ml

2 x 4 x 7.5 ml

More info
BIOPHEN AT (anti-IIa)   (CE-IVD) chromogenic method for in vitro quantitative determination of antithrombin (AT) activity, in presence of an excess of heparin,  using an anti-IIa method. Makes use of Bovine thrombin. 221122 2 x 2.5 ml More info
LIAPHEN AT (CE-IVD) a latex immunoassay for measuring Antithrombin (AT) in human citrated plasma, using a manual or an automated method, exclusively in vitro. 120002 Set of 2 x 40 tests


  1. Tsiang M et al. Functional requirements for inhibition of Thrombin by Antithrombin III in the presence and absence of heparin. The journal of Biological Chemistry vol. 272, N°18 12024-12029 (1997)
  2. Mann K.G. Biochemistry and Physiology of blood coagulation. Thrombosis and Haemostasis vol 82 N° 2 165-174 (1999).