1. Vanderbilt University School of Medicine, Nashville, Tennessee.
2. Division of Nephrology, Department of Medicine, Vanderbilt University Medical Center, Nashville, Tennessee.
3. Vanderbilt Center for Kidney Disease, Vanderbilt University Medical Center, Nashville, Tennessee.
4. Division of Epidemiology, Department of Medicine, Vanderbilt University Medical Center, Nashville, Tennessee.
5. Department of Biostatistics, Vanderbilt University Medical Center, Nashville, Tennessee.
6. Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania.