Division of Nephrology, Department of Medicine, Duke University School of Medicine, Durham, NC; Duke Clinical Research Institute, Duke University School of Medicine, Durham, NC; Renal Section, Durham VA Health Care System, Durham, NC. Section of Nephrology, Department of Pediatrics, Brenner Children's Hospital, Wake Forest School of Medicine, Winston Salem, NC; Division of Public Health Sciences, Department of Epidemiology and Prevention, Wake Forest School of Medicine, Winston Salem, NC; Department of Surgery-Hypertension and Vascular Research, Wake Forest School of Medicine, Winston Salem, NC; Cardiovascular Sciences Center, Wake Forest School of Medicine, Winston Salem, NC. Division of Nephrology, Department of Medicine, Duke University School of Medicine, Durham, NC; Renal Section, Durham VA Health Care System, Durham, NC. Renal-Electrolyte and Hypertension Division, Department of Medicine, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA; Department of Biostatistics, Epidemiology, and Informatics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA. Electronic address: jco@pennmedicine.upenn.edu.