**Core Concept:** Prothrombin Time (PT) and Activated Partial Thromboplastin Time (APTT) are global coagulation assays used to evaluate the intrinsic and extrinsic pathways of coagulation, respectively. An elevated PT and APTT indicate an underlying bleeding disorder or liver disease affecting coagulation factors.

**Why the Correct Answer is Right:** In this case, the elevated PT and APTT indicate a bleeding disorder, likely caused by a deficiency in vitamin K-dependent clotting factors. Vitamin K is an essential cofactor for the synthesis of these factors, which include II, VII, IX, X, protein C, and protein S. In the absence of these factors, the clotting cascade is disrupted, leading to prolonged coagulation times and an increased risk of bleeding.

**Why Each Wrong Option is Incorrect:**

A. Normal PT and APTT levels do not rule out vitamin K deficiency; other causes like liver disease or direct factor inhibitors can also cause elevated coagulation times.
B. Although vitamin K deficiency can cause the problem, this option is less likely due to the involvement of multiple clotting factors and the cascade of events.
C. This option is incorrect because vitamin K deficiency affects the synthesis of multiple clotting factors, leading to prolonged PT and APTT, not just Factor X deficiency.
D. This option is less likely due to the involvement of multiple clotting factors and the cascade of events.

**Clinical Pearl:** Vitamin K deficiency must be considered in young children with unexplained prolonged coagulation tests, especially those with a history of cholestasis or exposure to medications that interfere with vitamin K absorption (e.g., anticonvulsants). Early intervention with vitamin K supplementation can prevent significant bleeding complications.

**Correct Answer:** C. Vitamin K deficiency (Option C) is the correct answer because it affects the synthesis of multiple clotting factors, leading to prolonged PT and APTT. Vitamin K deficiency is a common cause of prolonged coagulation tests in children, especially those with a history of cholestasis or exposure to medications that interfere with vitamin K absorption. Early intervention with vitamin K supplementation can prevent significant bleeding complications.