The long-term goal is to assess the fall in kidney function measured by glomerular filtration rate (GFR) when patients with chronic kidney disease (CKD) are exposed to intravenous iron (IVIR). We hypothesize that in subjects with mild to moderate CKD, infusion of intravenous iron (IVIR), will generate oxidative stress and cause an inflammatory response that will be associated with a more rapid decline in glomerular filtration rate (GFR) compared to oral iron.