Hematology: Antithrombin-III Deficiency

Definition

• Definition: AT Activity Level < 80% of Normal
• AT-III Acts as an Anticoagulant & Inhibits Thrombin & Factor Xa
• Prevalence: 0.1-0.6%

Effects

• Increased Risk for VTE (Odds Ratio 16.3)
• Makes Heparin Ineffective

Diagnosis

• Diagnosis: AT-Heparin Cofactor Assay (Functional Coagulation Test)
• Indication for Testing:
  • VTE with Suspected Heparin Resistance
  • Thrombophilic Family (Strong Family History of VTE)
  • VTE at a Young Age (< 50 Years)
  • VTE in an Unusually Location (Portal/Hepatic/Mesenteric/Cerebral)
  • Recurrent VTE
• In General, If Testing Should Also Test for Other Inherited Thrombophilias
  • *See Hematology & Oncology: Factor V Leiden
  • *See Hematology & Oncology: Prothrombin G20210A
  • *See Hematology & Oncology: Protein C Deficiency
  • *See Hematology & Oncology: Protein S Deficiency

Management

• VTE Treatment: Anticoagulation – Similar to the General Population
• VTE Prevention: Generally Can Avoid Routine Chronic Anticoagulation Unless Otherwise Indicated or High-Risk