1. Fresenius Medical Care Polska S.A, Poznan, Poland
2. Fresenius Nephrocare Polska sp. z o.o, Poznan, Poland
3. 1st Department of Nephrology and Transplantology, Medical University of Bialystok, Białystok, Poland
4. Department of Nephrology, Dialysis and Internal Medicine, Medical University of Warsaw, Warszawa, Poland