Keep in mind IV contrast is also a diuretic so it is important to hydrate before and after the injection. In a patient without renal insuficency I am comfortable with PO hydration rather than IV.
We recently have been checking the GFR (glomerular filtration rate) in addition to the creatinine. If your lab is not reporting this you can go to www.nkdep.nih.gov and use the calculator. If the GFR is <60 the Rads will decide on before or after. At present they all want something different, but we are working on protocols.