1. Department of Internal Medicine and Nephrology, Medical Center Haaglanden, The Hague, the Netherlands
2. Department of Internal Medicine, Haga Teaching Hospital, The Hague, the Netherlands
3. Department of Nephrology, Leiden University Medical Center, Leiden, the Netherlands
4. Department of Internal Medicine, Diakonessenhuis, Utrecht, the Netherlands
5. Department of Clinical Chemistry, Haga Teaching Hospital, The Hague, the Netherlands