A 81 year old female with a history of pulmonary embolus is taking warfarin for anticoagulation. She is given antibiotics for pneumonia and has noted blood in her stool. Which of the following laboratory abnormalities would be expected?
A. Elevated activated partial thromboplastin time (PTT)
B. Elevated international normalized ratio (INR)
C. Elevated bleeding time
D. Elevated factor Xa assay