Participants are free to move around during the GFR test. At the conclusion of the GFR test, the second intravenous line will be removed. Subjects will remain at the CTRC for at least 30 minutes following removal of the IV line. During that time, nursing staff will re-measure and record the subject's vital signs (height, weight, blood pressure, temperature, pulse rate, respiration rate). The participants will be asked to void prior to leaving the CTRC to ensure complete urine collection over the study visit. The nurse will record the stop time of the urine collection. Upon successful completion of a study visit, subjects will receive a stipend.