[1] VA Med Ctr San Francisco, Div Nephrol, Dept Med, San Francisco, CA 94121 USA
[2] Univ Calif San Francisco, Dept Med, San Francisco, CA 94143 USA
[3] Univ Calif San Francisco, Dept Epidemiol & Biostat, San Francisco, CA 94143 USA
[4] George Washington Univ, Dept Med, Washington, DC 20052 USA