Which deficiency is indicated by a prolonged APTT?

A prolonged Activated Partial Thromboplastin Time (APTT) indicates an issue with the intrinsic pathway of coagulation or a deficiency in specific clotting factors involved in that pathway.

Factor IX deficiency, also known as Christmas disease, primarily affects the intrinsic pathway and results in a prolonged APTT. This is because Factor IX is essential for the proper functioning of the coagulation process that leads to the formation of a stable clot. When Factor IX is deficient, the body cannot effectively generate enough thrombin, leading to impairment in fibrin formation and subsequently prolonging the APTT test.

While Vitamin K deficiency and Factor VII deficiency can cause coagulopathy, they predominantly affect the extrinsic and common pathways. Thus, they do not specifically correlate with a prolonged APTT. Vitamin K is crucial for the synthesis of Factors II, VII, IX, and X, but its deficiency typically results in a prolonged Prothrombin Time (PT), more closely linked to the extrinsic pathway. Factor VII deficiency also results in a prolonged PT rather than APTT.

Factor VIII deficiency is associated with Hemophilia A and does lead to a prolonged APTT, but it is not the option provided as the selected answer. Factor IX is