The American College of Radiology has recently updated their guidelines for the use of metformin in patients receiving IV contrast media (11). A prior guideline recommended holding metformin for 4 days surrounding IV contrast administration to evaluate for contrast-induced acute kidney injury. This guideline contributed to the practice of discontinuing metformin during hospitalization due to the commonness of radiology studies using IV contrast. There is no drug interaction between metformin and contrast media nor is there any effect of metformin on renal function. Given the risk of contrast-induced acute kidney injury is very low in patients with normal renal function and no co-morbidities, the revised (2013) American College of Radiology guidelines recommend that metformin can be continued without the need to evaluate renal function following contrast media. In the presence of co-morbidities that increase the risk for developing acidosis (liver dysfunction, alcohol abuse, heart failure, myocardial or peripheral muscle ischemia, sepsis or severe infection), the new guidelines recommend holding metformin for two days after IV contrast administration. Our study will only include patients without these co-morbidities and with normal renal function (eGFR > 60 ml/min). All subjects will have serum creatinine measured daily, and metformin will be discontinued in the event of acute kidney injury.