Which statement best describes the laboratory pattern associated with vitamin K deficiency?

Which statement best describes the laboratory pattern associated with vitamin K deficiency?

• A. Prolonged PT with normal aPTT
• B. Prolonged aPTT with normal PT
• C. Both PT and aPTT prolonged
• D. Normal PT and aPTT

Answer: (A)

Vitamin K is required for activating several clotting factors (II, VII, IX, and X). The extrinsic pathway, which is reflected by the prothrombin time (PT), is most sensitive to vitamin K deficiency because factor VII has the shortest half-life. So, when vitamin K is deficient, PT becomes prolonged first while the intrinsic pathway (measured by aPTT) remains normal initially. This is why the best description of the lab pattern is a prolonged PT with a normal aPTT. If the deficiency is more severe or if other factors are affected, the aPTT may later become prolonged as well. In contrast, conditions like liver disease or DIC can prolong both PT and aPTT, and a normal PT and aPTT would suggest no significant vitamin K–dependent factor deficiency.

Vitamin K is required for activating several clotting factors (II, VII, IX, and X). The extrinsic pathway, which is reflected by the prothrombin time (PT), is most sensitive to vitamin K deficiency because factor VII has the shortest half-life. So, when vitamin K is deficient, PT becomes prolonged first while the intrinsic pathway (measured by aPTT) remains normal initially. This is why the best description of the lab pattern is a prolonged PT with a normal aPTT. If the deficiency is more severe or if other factors are affected, the aPTT may later become prolonged as well. In contrast, conditions like liver disease or DIC can prolong both PT and aPTT, and a normal PT and aPTT would suggest no significant vitamin K–dependent factor deficiency.