Factor VIII is decreased in which hemophilia?

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

Answer: (A)

Factor VIII deficiency defines Hemophilia A, the classic form. Factor VIII acts as a cofactor for activated Factor IX in the intrinsic coagulation pathway, forming the tenase complex with calcium and platelet surface phospholipids to activate Factor X. When Factor VIII is low, thrombin generation is impaired, leading to a bleeding tendency and a prolonged aPTT with a normal PT. Hemophilia A is X-linked recessive, primarily affecting males, and treated with desmopressin in mild cases or Factor VIII concentrate in more severe cases. The other factors listed correspond to different coagulation defects (Factor IX for Hemophilia B; Factor X or II deficiencies are separate disorders), not to Hemophilia A.