1. Department of Internal Medicine, Division of Nephrology, University of Groningen, University Medical Center Groningen, Groningen, the Netherlands
2. Diabetes Centre, Isala Clinics, Zwolle, the Netherlands
3. Langerhans Medical Research Group, Zwolle, the Netherlands
4. Department of Internal Medicine, University of Groningen, University Medical Center Groningen, Groningen, the Netherlands; the
5. Department of General Practice, University of Groningen, University Medical Center Groningen, Groningen, the Netherlands; and
6. B.R.A.H.M.S. GmbH, Thermo Fisher Scientific, Hennigsdorf, Germany.