“How long do you have to stop metformin before a CT scan?”

Metformin stoppage for CT is only with CTs that use intravenous contrast. Stoppage extends for 48 hours after the procedure and its IV contrast usage. Knowledge of the exact requested exam via the ordering clinician and the radiologist in charge of the exam is necessary. Each institution has their particular protocols. Discussions with your physician as to whether a substitute for metformin is desired during the preCT and post exam "48 hours" should be had.

Harris L. Cohen, MD, FACR