Which pattern of coagulation test abnormalities is typical in vitamin K deficiency?

Which pattern of coagulation test abnormalities is typical in vitamin K deficiency?

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

Answer: (B)

Vitamin K is needed to gamma-carboxylate factors II, VII, IX, and X. Because factor VII has the shortest half-life, a deficiency most quickly disrupts the extrinsic pathway, which is reflected as a prolonged prothrombin time (PT). The intrinsic pathway (measured by aPTT) remains normal early on because those factors are less affected initially. So the typical pattern in vitamin K deficiency is a prolonged PT with a normal aPTT. If deficiency is severe, both PT and aPTT can become prolonged as more factors decline. Other patterns point to different issues, such as intrinsic pathway disorders causing prolonged aPTT with normal PT, or overall severe deficiency or liver/DIC causing both tests to be prolonged, or normal tests suggesting no significant coagulation factor deficiency.

Vitamin K is needed to gamma-carboxylate factors II, VII, IX, and X. Because factor VII has the shortest half-life, a deficiency most quickly disrupts the extrinsic pathway, which is reflected as a prolonged prothrombin time (PT). The intrinsic pathway (measured by aPTT) remains normal early on because those factors are less affected initially. So the typical pattern in vitamin K deficiency is a prolonged PT with a normal aPTT. If deficiency is severe, both PT and aPTT can become prolonged as more factors decline. Other patterns point to different issues, such as intrinsic pathway disorders causing prolonged aPTT with normal PT, or overall severe deficiency or liver/DIC causing both tests to be prolonged, or normal tests suggesting no significant coagulation factor deficiency.