[1] Salford Royal Hosp, Dept Renal Med, Salford, Lancs, England
[2] US Renal Data Syst Coordinating Ctr, Minneapolis, MN USA
[3] Minneapolis Vet Affairs Med Ctr, Dept Med, Nephrol Sect, Minneapolis, MN USA
[4] Univ Minnesota, Dept Med, Minneapolis, MN 55455 USA