Which laboratory finding is characteristic of vitamin K deficiency?

Which laboratory finding is characteristic of vitamin K deficiency?

• A. Prolonged PT with normal bleeding time
• B. Prolonged PT only
• C. Prolonged PT and aPTT
• D. Normal PT and aPTT

Answer: (A)

Vitamin K is needed to activate several clotting factors (II, VII, IX, and X). When vitamin K is deficient, those factors are undercoagulated, and the extrinsic pathway is affected first because factor VII has the shortest half-life. That shows up as a prolonged prothrombin time (PT). Bleeding time reflects platelet function, which isn’t impacted by vitamin K status, so it remains normal. The intrinsic pathway (aPTT) may stay normal early on and only lengthen later if the deficiency worsens. So the hallmark lab pattern is a prolonged PT with a normal bleeding time.

Vitamin K is needed to activate several clotting factors (II, VII, IX, and X). When vitamin K is deficient, those factors are undercoagulated, and the extrinsic pathway is affected first because factor VII has the shortest half-life. That shows up as a prolonged prothrombin time (PT). Bleeding time reflects platelet function, which isn’t impacted by vitamin K status, so it remains normal. The intrinsic pathway (aPTT) may stay normal early on and only lengthen later if the deficiency worsens. So the hallmark lab pattern is a prolonged PT with a normal bleeding time.