Factor XII deficiency is associated with which of the following true statements?

• A. It usually causes severe bleeding
• B. It prolongs the aPTT but does not cause mucosal bleeding
• C. It shortens the aPTT
• D. It is diagnosed by an abnormal PT

Answer: (B)

Factor XII is part of the contact activation system that starts the intrinsic coagulation cascade in laboratory testing. When this factor is deficient, the aPTT becomes prolonged because the test’s activation step can’t start efficiently. But in the body, coagulation can proceed without relying on Factor XII, so there isn’t an associated bleeding tendency. This means the aPTT is longer in the test, yet patients don’t typically have mucosal bleeding. The PT remains normal because the extrinsic pathway isn’t affected by Factor XII. So the statement that Factor XII deficiency prolongs the aPTT but does not cause mucosal bleeding is the most accurate reflection of how this deficiency behaves clinically.