Hemophilia B is caused by deficiency of which clotting factor?

Hemophilia B is caused by deficiency of which clotting factor?

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

Answer: (C)

Hemophilia B is a deficiency in a protein of the intrinsic coagulation pathway. Specifically, it’s a lack of Factor IX, also known as Christmas factor. Factor IX normally helps activate Factor X to kick off the downstream steps that generate thrombin and form a stable clot. When Factor IX is missing, clot formation is impaired, leading to easy or excessive bleeding, especially into joints and muscles. In lab tests, the intrinsic pathway is slow, so the partial thromboplastin time is prolonged, while the extrinsic pathway (and PT) is typically normal because Factor VII is unaffected. If Factor VIII were deficient, you’d have Hemophilia A, not B. If Factor VII were deficient, it would disrupt the extrinsic pathway and prolong PT. If Factor X were deficient, the issue would arise in the common pathway and cause widespread coagulation problems. Hence, the correct factor in Hemophilia B is Factor IX.

Hemophilia B is a deficiency in a protein of the intrinsic coagulation pathway. Specifically, it’s a lack of Factor IX, also known as Christmas factor. Factor IX normally helps activate Factor X to kick off the downstream steps that generate thrombin and form a stable clot. When Factor IX is missing, clot formation is impaired, leading to easy or excessive bleeding, especially into joints and muscles. In lab tests, the intrinsic pathway is slow, so the partial thromboplastin time is prolonged, while the extrinsic pathway (and PT) is typically normal because Factor VII is unaffected.

If Factor VIII were deficient, you’d have Hemophilia A, not B. If Factor VII were deficient, it would disrupt the extrinsic pathway and prolong PT. If Factor X were deficient, the issue would arise in the common pathway and cause widespread coagulation problems. Hence, the correct factor in Hemophilia B is Factor IX.