The CKiD Study is a multi-center, prospective cohort study of children aged 1 to 16 years with mild to moderate impaired kidney function. Two clinical coordinating centers at Children's Mercy Hospital in Kansas and at Johns Hopkins School of Medicine, a central laboratory at the University of Rochester, and a data coordinating center at Johns Hopkins School of Public Health have formed a cooperative agreement to conduct a prospective study of chronic kidney disease in children. 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; growth failure and its associated morbidity; and neurocognitive function and behavior.

Inclusion Criteria:

• Age between 1 and 16 years (before 17th birthday)
• Estimated (based on SCr) GFR between 30 and 75 ml/min/1.73m2
• Willingness and ability to provide informed consent and assent

Exclusion Criteria:

• Renal, other solid organ, bone marrow or stem cell transplantation
• Dialysis treatment within the past three months
• Cancer/leukemia diagnosis or HIV diagnosis/treatment within last twelve months
• Current pregnancy or pregnancy within past twelve months
• Inability to complete major data collection procedures (e.g., allergic reaction to iodine or Iohexol)
• Current enrollment in a randomized clinical trial in which the specific treatment is unknown
• 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 they move)
• History of structural heart disease
• Genetic syndromes involving the central nervous system (e.g., Downs syndrome)
• History of severe to profound mental retardation (i.e., IQ<40, significant impairment in adaptive function and/or inability to independently execute self-care skills)