Esther Meijer1, Ron T Gansevoort2. 1. Division of Nephrology, Department of Internal Medicine, University Medical Center Groningen, University of Groningen, Groningen, the Netherlands. Electronic address: esther.meijer@umcg.nl. 2. Division of Nephrology, Department of Internal Medicine, University Medical Center Groningen, University of Groningen, Groningen, the Netherlands.