Hemophilia A is caused by deficiency of which clotting factor?

Hemophilia A is caused by deficiency of which clotting factor?

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

Answer: (A)

Hemophilia A is caused by a deficiency of Factor VIII, a crucial cofactor in the intrinsic coagulation pathway. Factor VIII works with activated Factor IX (IXa) to form the tenase complex that activates Factor X. Without enough Factor VIII, this amplification step is impaired, leading to insufficient thrombin generation and a tendency for bleeding, especially into joints and deep tissues. Clinically, this condition is X-linked recessive and typically presents with a prolonged aPTT and a normal PT. If Factor IX were deficient, you’d have a similar bleeding pattern (Hemophilia B), since both affect the intrinsic pathway, but it’s due to Factor IX rather than Factor VIII. A deficiency of Factor VII would prolong the PT because it affects the extrinsic pathway. A deficiency of Factor X would disrupt both pathways, often prolonging both PT and aPTT.

Hemophilia A is caused by a deficiency of Factor VIII, a crucial cofactor in the intrinsic coagulation pathway. Factor VIII works with activated Factor IX (IXa) to form the tenase complex that activates Factor X. Without enough Factor VIII, this amplification step is impaired, leading to insufficient thrombin generation and a tendency for bleeding, especially into joints and deep tissues. Clinically, this condition is X-linked recessive and typically presents with a prolonged aPTT and a normal PT.

If Factor IX were deficient, you’d have a similar bleeding pattern (Hemophilia B), since both affect the intrinsic pathway, but it’s due to Factor IX rather than Factor VIII. A deficiency of Factor VII would prolong the PT because it affects the extrinsic pathway. A deficiency of Factor X would disrupt both pathways, often prolonging both PT and aPTT.