A 7-year-old child with prolonged PT and normal aPTT is being evaluated before ear tube surgery. Which condition is most likely?

A 7-year-old child with prolonged PT and normal aPTT is being evaluated before ear tube surgery. Which condition is most likely?

• A. Vitamin K deficiency
• B. Hemophilia A
• C. von Willebrand disease
• D. Factor II deficiency

Answer: (A)

Prolonged PT with a normal aPTT points to a problem in the extrinsic pathway, most commonly a deficiency of factor VII or a vitamin K–dependent deficiency affecting factors II, VII, IX, and X. Vitamin K is essential for activating these factors; because factor VII has the shortest half-life, its activity drops first, lengthening the PT while the intrinsic pathway factors (which influence the aPTT) are still sufficient. In a 7-year-old being evaluated before surgery, this pattern fits vitamin K deficiency best, as it directly delays the extrinsic pathway without initially disturbing the intrinsic pathway. Hemophilia A would prolong the aPTT (intrinsic pathway) rather than the PT; von Willebrand disease can affect bleeding but does not classically produce isolated PT prolongation; and a deficiency of factor II would typically prolong both PT and aPTT since it lies in the common pathway.

Prolonged PT with a normal aPTT points to a problem in the extrinsic pathway, most commonly a deficiency of factor VII or a vitamin K–dependent deficiency affecting factors II, VII, IX, and X. Vitamin K is essential for activating these factors; because factor VII has the shortest half-life, its activity drops first, lengthening the PT while the intrinsic pathway factors (which influence the aPTT) are still sufficient. In a 7-year-old being evaluated before surgery, this pattern fits vitamin K deficiency best, as it directly delays the extrinsic pathway without initially disturbing the intrinsic pathway. Hemophilia A would prolong the aPTT (intrinsic pathway) rather than the PT; von Willebrand disease can affect bleeding but does not classically produce isolated PT prolongation; and a deficiency of factor II would typically prolong both PT and aPTT since it lies in the common pathway.