Which coagulation parameter pattern is typical of vitamin K deficiency?

Which coagulation parameter pattern is typical of vitamin K deficiency?

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

Answer: (B)

Vitamin K is required for gamma-carboxylation of clotting factors II, VII, IX, and X (and proteins C and S). When vitamin K is deficient, these factors are reduced and the coagulation cascade slows in both the extrinsic and intrinsic pathways. PT measures the extrinsic pathway (factor VII) and the common pathway, while aPTT measures the intrinsic pathway (factors VIII, IX, XI, XII) and the common pathway. With deficiencies in multiple vitamin K–dependent factors, both PT and aPTT become prolonged. Bleeding time, which reflects platelet function, remains normal because platelets aren’t directly affected by vitamin K status. So the typical pattern is prolonged PT and prolonged aPTT with a normal bleeding time. If only PT were prolonged, that could reflect an earlier or milder deficiency or warfarin effect; if bleeding time were prolonged, that would suggest a platelet problem rather than a coagulation factor issue.

Vitamin K is required for gamma-carboxylation of clotting factors II, VII, IX, and X (and proteins C and S). When vitamin K is deficient, these factors are reduced and the coagulation cascade slows in both the extrinsic and intrinsic pathways. PT measures the extrinsic pathway (factor VII) and the common pathway, while aPTT measures the intrinsic pathway (factors VIII, IX, XI, XII) and the common pathway. With deficiencies in multiple vitamin K–dependent factors, both PT and aPTT become prolonged. Bleeding time, which reflects platelet function, remains normal because platelets aren’t directly affected by vitamin K status. So the typical pattern is prolonged PT and prolonged aPTT with a normal bleeding time. If only PT were prolonged, that could reflect an earlier or milder deficiency or warfarin effect; if bleeding time were prolonged, that would suggest a platelet problem rather than a coagulation factor issue.