1. Department of Laboratory Medicine, Radboud University Medical Centre, Nijmegen, The Netherlands
2. Department of Laboratory for Clinical Chemistry, Part of Result Laboratorium, Amphia Hospital, Breda, The Netherlands
3. SKML, Organisation for Quality Assurance of Medical Laboratory Diagnostics, Radboud University, Nijmegen, The Netherlands
4. Department of Nephrology, Radboud University Medical Centre, Radboud Institute for Health Sciences, Nijmegen, The Netherlands