 The administration of inulin will be considered time 0. Following the iohexol administration, blood samples will be taken at approximately 10, 30, 120, and 240 minutes from the second intravenous line. For participants with estimated GFR less than 45 mlmin per 1.73 m2, as determined from the screening visit or the subjects medical record, a sample will be drawn at 360 minutes. The exact time of the sample will be recorded. 