In Hemophilia A, which factor is deficient?

In Hemophilia A, which factor is deficient?

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

Answer: (C)

Factor VIII deficiency defines Hemophilia A. Factor VIII acts as a cofactor for activated Factor IX (IXa) in the tenase complex, which is essential for converting Factor X to Xa and generating thrombin. Without enough Factor VIII, the intrinsic pathway cannot effectively drive clot formation, leading to easy and recurrent bleeding, especially into joints and muscles, and a prolonged aPTT with a normal PT. This distinguishes it from other bleeding disorders: a deficiency of Factor IX causes Hemophilia B, Factor XI deficiency causes Hemophilia C, and a deficiency of Factor VII affects the extrinsic pathway and PT. Treatments include desmopressin to release stored Factor VIII in milder cases and Factor VIII replacement for more severe disease.

Factor VIII deficiency defines Hemophilia A. Factor VIII acts as a cofactor for activated Factor IX (IXa) in the tenase complex, which is essential for converting Factor X to Xa and generating thrombin. Without enough Factor VIII, the intrinsic pathway cannot effectively drive clot formation, leading to easy and recurrent bleeding, especially into joints and muscles, and a prolonged aPTT with a normal PT. This distinguishes it from other bleeding disorders: a deficiency of Factor IX causes Hemophilia B, Factor XI deficiency causes Hemophilia C, and a deficiency of Factor VII affects the extrinsic pathway and PT. Treatments include desmopressin to release stored Factor VIII in milder cases and Factor VIII replacement for more severe disease.