Medicine & USMLE

Antithrombin-3 Deficiency

  1. Common Pathway of Coagulation
  2. Extrinsic Pathway of Coagulation
  3. Intrinsic Pathway of Coagulation
  4. Hemophilia A
  5. Hemophilia B
  6. Hemophilia C
  7. Factor V Leiden
  8. Antithrombin-3 Deficiency


Antithrombin-3 Deficiency is a blood clotting disorder caused by abnormally low levels of antithrombin 3. This condition can be inherited in an autosomal dominant pattern, but may also be acquired secondary to renal or liver failure. Affected patients typically present with recurrent blood clots, such as deep vein thrombosis or pulmonary embolism. Finally, a distinctive lab finding of antithrombin 3 deficiency is a diminished increase in PTT following the administration of heparin.

Key Points

  • Antithrombin-3 Deficiency
    • Pathogenesis
      • Inherited deficiency of antithrombin-3
        • Antithrombin 3 usually works to inhibit factors IIa and Xa
        • Decreased inhibition of factors IIa and Xa → hypercoagulability
      • May be acquired
        • Renal failure or nephrotic syndrome
          • Loss of antithrombin-3 in the urine
        • Liver failure
          • Inability to produce antithrombin-3 in the liver
    • Genetics
      • Autosomal dominant inheritance
    • Presentation
      • Recurrent thrombosis (clots)
        • Especially at a young age in otherwise healthy individual
        • Venous > arterial
        • DVT
        • PE
    • Diagnosis
      • Normal PT, PTT, thrombin time
        • No direct effect on secondary hemostasis as measured in the laboratory setting
      • Diminished increase in PTT after heparin administration
    • Treatment
      • Anticoagulants as needed for thrombosis
      • Antithrombin replacement therapy