Inclusion Criteria:  matching to one of the following groups CKD G3-5: estimated eGFR according to Schwartz formula <60ml/min*1,73m2 (no ESKD) CKD G5 D: patients with ESKD treated with hemodialysis for at least 3 months normal kidney function: CKD G1 or no CKD with eGFR > 90ml/min*1,73m2 informed consent to participate in this study  Exclusion Criteria:  body weight of less than 15kg acute or chronic inflammatory diseases fever diabetes chronic liver disease inflammatory bowel disease or other gastrointestinal disorders (constipation, diarrhea, short bowel syndrome) antibiotic prophylaxis or treatment within four weeks prior to recruitment