It is well known that X-ray contrast media can affect kidney function in some patients, especially when administered intra-arterially, and patients who already suffer from reduced kidney function and diabetes mellitus may be at increased risk. It is widely accepted to use low-osmolar or iso-osmolar contrast media, especially in patients at risk for contrast media-induced nephropathy. However, little is known about the intravenous use of X-ray contrast media in risk patients, such as contrast-enhanced CT examinations. The main purpose of this study is to evaluate and compare the effects on kidney function of two contrast media, the iso-osmolar iodixanol and the low-osmolar iopamidol in patients at risk of kidney damage associated with the injection of contrast media. Due to the iso-osmolar feature, it is expected less influence on renal function following administration of iodixanol. A standard hydration procedure, based on available guidelines will be given to all patients to prevent negative effects on the kidneys. Serum creatinine (SCr ) concentrations will be measured before and up to 7 days after contrast media administration to evaluate the effects on renal function.