Inclusion Criteria:  i) Group 1 (patients < 18 years of age)- obtaining reference values without any of the pre-defined events  renal transplant patients with stable renal function parameters (mean SCr (or cystatin C) or mean eGFR based on creatinine and / or cystatin C defined as changes ≤ ±15 % for at least three consecutive ambulatory controls). patients with CKD IV-V (and maintained urine output, without renal replacement therapy and without pre-defined events). healthy controls.  Study patients from group 1 may be assigned to the group 2 in the following conditions:  ii) Group 2 (patients < 18 years of age)- obtaining biomarker-specific characteristic in the presence of any of the pre-defined events  renal transplant recipients with living or deceased kidney transplantation. patients with CKD IV-V (and maintained urine output without renal replacement therapy). healthy controls.  Exclusion Criteria:  i) Healthy controls  any comorbidity / medication which may have an impact on urinary biomarker profile (e.g. primary kidney or liver disease, metabolic disease, vasculitis or other immunological disease other than the pre-defined events). for group 1: presence of any of the pre-defined event. ii) CKD IV-V any comorbidity / medication which may have an impact on urinary biomarker profile (e.g. liver disease, metabolic disease, vasculitis or other immunological disease other than the pre-defined events). for group 1: presence of any of the pre-defined event. iii) Renal transplant patients for group 1: presence of any of the pre-defined event. Primary non-function of the renal transplant organ. Blood group (AB0) incompatible. Detection of donor specific antibody (DSA) positive (panel-reactive antibodies) at time of enrolment. any comorbidity / medication which may have an impact on urinary biomarker profile (e.g. liver disease, metabolic disease, vasculitis or other immunological disease) other than the pre-defined events. Presence of other transplanted organs or co-transplanted organs. Intention to not use a standard maintenance immunosuppression regimen consisting of calcineurin inhibitor (CNI), antimetabolite (mycophenolate or azathioprine), inhibitor of mechanistic target of rapamycin (mTOR) (Sirolimus / Everolimus) with/without corticosteroids. Any condition that, in the opinion of the investigator, would pose risk to the subject's safe participation, or interfere with their ability to comply with the study requirements, or may impact the quality of the interpretation of the data (e.g. detection of malignancy). Failure to collect urine samples or incomplete additional CERTAIN dataset (for collecting information about pre-defined events).