A patient is stabilized on warfarin with an international normalized ratio (INR) of 2.7. He develops pneumonia and is admitted to the hospital. His appetite is depressed and he is placed on broad-spectrum antibiotic agents

At 1 week after the admission, his INR is 5.0. What is the most likely interpretation?

a. The patient should be given more warfarin.
b. A PTT should be performed to rule out heparin administration.
c. A new sample should be collected to rule out a clotted specimen.
d. Vitamin K is reduced, increasing the effects of warfarin.

ANS: D
This elevated INR is probably the result of a deficiency of vitamin K, which increases the effects of warfarin. Vitamin K deficiency is seen during use of broad-spectrum antibiotic agents that destroy gut flora and in people with a poor diet, both of which are present in this patient.