[1] Toensberg Cty Hosp, Dept Med, Renal Sect, N-3103 Tonsberg, Norway
[2] Clin Inst Med & Chem Lab Diagnost, Graz, Austria
[3] Univ Oslo, Ullevaal Hosp, Dept Prevent Med, N-0407 Oslo, Norway
[4] Univ Oslo, Ullevaal Hosp, Clin Res Ctr, N-0407 Oslo, Norway
[5] Synlab Med Versorgungzentrum Labordiagnost Heidel, Heidelberg, Germany
[6] Med Univ Graz, Clin Inst Med & Chem Lab Diag, Graz, Austria
[7] Univ Hosp, Dept Med Sci, Renal Unit, Uppsala, Sweden
[8] Western Infirm Hosp, Dept Med & Therapeut, Glasgow, Lanark, Scotland
[9] Univ Oslo, Rikshosp, Dept Med, Oslo Univ Hosp, N-0027 Oslo, Norway