Acquired hemophilia is caused by inhibitors against which coagulation factor?

• A. Factor IX
• B. Factor VIII
• C. Factor VII
• D. Factor X

Answer: (B)

Acquired hemophilia occurs when autoantibodies develop that neutralize a coagulation factor, most classically Factor VIII. Blockading Factor VIII prevents formation of the intrinsic tenase complex (with Factor IXa) that is essential to efficiently activate Factor X, so thrombin generation drops and clot formation falters. This yields a bleeding tendency with a prolonged aPTT while the PT remains normal. Clinically, adults often have spontaneous soft-tissue or mucosal bleeding rather than joint bleeding, which helps distinguish it from congenital forms. Diagnosis is guided by an isolated prolonged aPTT with normal PT and is confirmed by assays showing reduced Factor VIII activity along with detectable inhibitors.