Loss of antithrombin III predisposes to a hypercoagulable state leading to what complication?

• A. Thrombosis or thromboembolism
• B. Bleeding tendency
• C. Renal failure
• D. Seizures

Answer: (A)

Losing antithrombin III removes a key brake on coagulation. Antithrombin III is a natural anticoagulant that inhibits thrombin and factor Xa, among others. When its activity is reduced, thrombin generation is less restrained, shifting the balance toward clot formation. This creates a hypercoagulable state, making thrombosis or thromboembolism the most likely complication (such as deep vein thrombosis or pulmonary embolism). Bleeding tendencies are not expected from ATIII deficiency, since the problem is excessive clotting, not insufficient clot formation. Renal failure and seizures aren’t direct consequences of ATIII deficiency.