1 Territorial Department of Nephrology and Dialysis, ASL 8, Cagliari, Italy - pg.bolasco@tin.it.
2 Division of Nephrology and Hypertension, Harold Simmons Center for Kidney Disease Research and Epidemiology, University of California Irvine Medical Center, Orange, CA, USA.
3 Department of Epidemiology, UCLA Fielding School of Public Health, Los Angeles, CA, USA.