The latest guidelines from the Royal College of Radiologists (2009)

If the serum creatinine is normal, and a low volume of contrast agent (up to 100ml) is to be administered intravenously, no special precaution is required.  This is the case except in CT angiograms.

If the serum creatinine is normal , but more than 100ml of contrast agent or intra-arterial route is used , Metformin should be withheld for 48 hours after the procedure.

If the serum Creatinine is raised , the need for contrast should be re-assessed. If deemed necessary Metformin should be withheld for 48 hours before and 48 hours after the contrast is given and the renal function re-assessed before restarting the Metformin treatment. Metformin should be restarted if the results of the U & Es are unchanged.If there is a deterioration in renal function then Metformin should not be restarted until after discussion with the patients’  General Practitioner/ referring doctor/ Diabetes Team.Other treatment may be required in the interim. 

 All patients with diabetes should have a measurement of their creatinine on at least an annual basis. If this has not taken place a measurement should be done fbefore the procedure and this is the responsibility of the referring cliniician.