Hydration with intravenous normal saline has consistently been shown to prevent or ameliorate contrast induced renal impairment in patients with and without existing renal disfunction.[30–32] Hydration prevents CIN by increasing the glomerular filtration rate by plasma volume expansion and suppressing renin–angiotensin system, thereby down regulating the tubulo-glomerular feed back mechanism.[33] Iodinated contrast agents increase urine flow and osmolar clearance resulting in a prolonged dehydrated state.[34] Hydration prevents CIN by ameliorating the effect of contrast agents. This evidence concerns the gene REN and cervical squamous intraepithelial neoplasia.