DEFICIENCY OF ANTITHROMBIN III

• Biochemical aspects:
  • Antithrombin III (AT III), also known as heparin cofactor, consists of a single polypeptide chain with a molecular weight of about 65,000. AT III inhibits not only thrombin but also the other serine proteases of coagulation, including factors XIIa, XIa, IXa, Xa, and perhaps VIIa.
  • AT III's inhibitory activity is strikingly accelerated in the presence of heparin.
• Pathological Basis:
  • Mode of inheritance: autosomal dominant.
  • Typically, there is a strong family history of venous thromboembolic disease. Often, patients appear to be resistant to heparin anticoagulation.
  • Acquired deficiency of AT III may be seen in patients with nephrotic syndrome secondary to massive proteinuria.
• Treatment:
  • Long-term oral anticoagulant therapy.
  • For short-term replacement therapy: FFP or AT III concentrates (available in Europe).
  • Anabolic steroids may be helpful in hereditary deficiency of AT III.