The Division of Kidney, Urologic, and Hematologic Diseases (DKUHD) of the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), in collaboration with the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) and the National Heart, Lung and Blood Institute (NHLBI) funded a cooperative agreement including two Clinical Coordinating Centers (at Children's Hospital of Philadelphia and at Children's Mercy Hospital in Kansas City), a central biochemistry laboratory (at the University of Minnesota) and a Data Coordinating Center (at Johns Hopkins School of Public Health) to conduct a prospective epidemiological study of children with chronic kidney disease (CKD).

Since its inception in 2003, the scientific aims of CKiD have been to determine the risk factors for decline in kidney function and to define how progressive decline in kidney function impacts biomarkers of risk factors for cardiovascular disease; neurocognitive function and behavior; and growth failure and its associated morbidity.

The goals have been extended to understand the impact of childhood CKD on: the risk factors for decline in kidney function in childhood and young adulthood; the development of cardiovascular disease in adolescence and young adulthood; the trajectories of markers of metabolic bone disease and the relationship to cardiovascular endpoints; and the social function, neurocognitive function and emotional well-being of adolescents and young adults and the relationship to successful transfer to adult nephrology care.

Inclusion Criteria:

• Age between 1 and 16 years (before 17th birthday) for Cohorts 1 and 2; age between 6 months and 16 years (before 17th birthday) for Cohort 3; age between 16 to 22 years (before 23rd birthday) for Cohort 4
• Estimated (based on SCr) Schwartz GFR between 30 and 90 ml/min|1.73m2 for Cohort 1 OR an estimated GFR between 45 and 90 ml/min|1.73m2 based on the updated Schwartz formula for Cohort 2; an estimated GFR ≤60 based on the CKiD Under 25 estimating equation (U25eGFR) OR KRT experience (dialysis or transplant) for Cohort 4
• Willingness and ability to provide informed consent and assent
• For Cohort 3, children with non-glomerular diagnosis and duration of kidney disease less than 5 years will be enrolled.

Exclusion Criteria:

• Solid organ (other than kidney), bone marrow or stem cell transplantation
• Cancer diagnosis and receiving treatment or within 12 months post completion of treatment
• Ongoing monitoring for cardiotoxic effects of prior chemotherapy or targeted cancer therapies (e.g., anthracyclines, trastuzumab)
• HIV infection with detectable viral load despite current antiretroviral therapy
• Current pregnancy or pregnancy within past twelve months
• Inability to complete major data collection procedures
• Not fluent in English or Spanish
• Plans to move out of area of any participating CKiD site (families can be transferred to another CKiD site if the family moves)
• Existing moderate to severe congenital structural heart disease
• Genetic syndromes involving the central nervous system (e.g., Downs syndrome)
• History of severe to profound intellectual disability (i.e., Intelligence Quotient (IQ)<40, significant impairment in adaptive function and/or inability to independently execute self-care skills)
• For cohort 3, children who are expected to receive renal replacement therapy within 6 months of date of enrollment will not be recruited

The CKiD Study is a multi-center, prospective cohort study of children, adolescents and young adults with a history of mild to moderate impaired kidney function. The study population consist of four cohorts.