[1] Virginia Commonwealth Univ, Dept Pathol, Richmond, VA USA
[2] Univ Virginia, Sch Med, Dept Pathol, Charlottesville, VA 22908 USA
[3] NIH, Dept Lab Med, Warren G Magnuson Clin Ctr, Bethesda, MD 20892 USA
[4] Norwegian Qual Improvement Lab Serv Primary Care, NOKLUS, Bergen, Norway
[5] Haukeland Hosp, Lab Clin Biochem, Bergen, Norway
[6] McMaster Univ, Dept Pathol & Mol Med, Hamilton Reg Lab, Program Med, Hamilton, ON, Canada
[7] Asahikawa Med Coll, Dept Lab Med, Asahikawa, Hokkaido 078, Japan
[8] Mayo Clin, Renal Funct Lab, Dept Lab Med & Pathol, Div Nephrol & Hypertens,Dept Internal Med, Rochester, MN USA
[9] Univ British Columbia, Canadian External Qual Assessment Lab, Vancouver, BC V5Z 1M9, Canada
[10] Univ British Columbia, Dept Pathol & Lab Med, Vancouver, BC V5Z 1M9, Canada
[11] St Vincents Hosp Sydney, Dept Chem Pathol, Sydney, NSW, Australia
[12] Natl Inst Stand & Technol, Div Analyt Chem, Gaithersburg, MD 20899 USA
[13] Harvard Univ, Brigham & Womens Hosp, Sch Med, Dept Med,Renal Div, Boston, MA 02115 USA
[14] Natl Inst Diabet & Digest Dis, Natl Kidney Dis Educ Program, NIH, Bethesda, MD USA