Updated: 3/16/2018

Antithrombin III Deficiency

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Snapshot
  • A 23-year-old girl presents to the emergency room with shortness of breath, pleuritic chest pain, and hemoptysis. She is found to be tachycardic; her pulse is 102/min. She has a history of DVTs requiring heparin at age 20. However, she has not been on any maintenance therapy. Clinical suspicion for a pulmonary embolism is high, and a chest spiral CT scan is ordered.  The CT shows a saddle embolism. Heparin is started immediately.
Introduction

  • Pathogenesis
    • hypercoagulable state/thrombophilia due to deficiency in antithrombin III
    •  
      • antithrombin III, an anticoagulant
        • inhibits primarily thrombin (factor IIa) and factor Xa
        • also inhibits activated factors VII, IX, XI, and XII
        • remember, heparin enhances activity of antithrombin
      • deficiency causes defect in anticoagulation pathway
  • Genetics
    • autosomal dominant inheritance 
  • Risk factors
    • liver disease (antithrombin III is synthesized in the liver)
    • renal failure/nephrotic syndrome (loss of proteins in urine)
    • heparin use (causes acquired reduction in antithrombin level)
Presentation
  • Symptoms/physical exam
    • may be asymptomatic
    • thrombosis at a young age (venous > arterial)
      • DVT
      • PE
Evaluation
  • Normal PT, PTT, and thrombin time
  • Reduces the increase in PTT following heparin administration
  • Heparin cofactor assay, an antithrombin functional assay
    • ↓ antithrombin activity
Differential Diagnosis
  • HIT
  • Protein C/S deficiency
  • Factor V Leiden mutation
Treatment
  • For acute thrombosis
    • heparin
  • For maintenance therapy
    • bridge to warfarin
  • Medical therapy
    • antithrombin replacement therapy
      • peripartum and perioperative
Prognosis, Prevention, and Complications
  • Prognosis
    • at risk of thromboembolism
      • lifetime risk 50-85%
  • Prevention
    • avoid pro-coagulant states
      • OCPs
      • hormone replacement therapy
  • Complications
    • related to thromboembolism

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