1. Prepared by Kelly Craven, MD, PhD and reviewed by Ivo Francischetti, MD, PhD.

A elderly patient presented with right upper extremity weakness and facial droop and was found to have a distal left posterior division M3 branch occlusion on a CT Head. The patient was given tPA. PT and INR were normal on admission, but they subsequently became prolonged to 25.8 s (ref: 9.6-11.8) and 2.54 (ref: 0.9-1.1), respectively. The patient was not taking any anticoagulants. Thrombin time was 34.7 s (ref: 17.5-20.6). Fibrinogen was <35 mg/dL (ref: 150-450). D-Dimer was 18.41 mg/L (ref: 0-0.49). Platelets were 350 K/cu mm (ref: 150-350).


Based on the information provided, what is the MOST likely reason the PT/INR is prolonged?