Chronic kidney disease (CKD) is a life-long condition that often results in substantial morbidity and premature death due to complications from a progressive decrease in kidney function. The early detection of, and initiation of therapy for, CKD is key to delaying or preventing progression to end-stage renal disease (ESRD). The CKiD (Chronic Kidney Disease in Children, https://statepi.jhsph.edu/ckid/) study is a prospective cohort study of children with CKD that investigates risk factors and outcomes of the disease.

The study population consists of two cohorts. Cohort 1 includes 586 racially and ethnically diverse children recruited between the ages of 1 and 16 years with mild to moderately impaired kidney function (defined by an estimated GFR between 30-90 ml/min/1.73m²). Cohort 2 includes 305 children with mildly impaired kidney function (defined as an estimated GFR between 45-90 ml/min/1.73m²). At baseline, participants underwent a physical examination, in addition to assessments of kidney, cardiovascular, and neurocognitive symptoms and function. Similar measures of kidney function, neurocognitive function, markers of risk factors for cardiovascular disease, growth and other co-morbid conditions are assessed at regularly scheduled study visits. Biospecimens, including serum, plasma, and urine are also collected. The primary outcome measure is the rate of decline of GFR, which is measured repeatedly over time in cohort participants. A secondary outcome measure is the time to ESRD, defined by transplantation, dialysis, or a 50% decrease in GFR.

Baseline and follow-up biospecimens and data through July 31, 2018 are available from the Repository. The most recent data contains additional summary files related to nutrients and grip strength.

The CKiD study had various objectives, including: (1) identifying and quantifying novel and traditional risk factors for progression of CKD; (2) characterizing how CKD progression effects neurodevelopment, cognitive abilities, and behavior; (3) describing the prevalence of cardiovascular disease and associated risk factors; and (4) examining the effects of declining kidney function on growth in children with CKD.

The primary outcome measure is the rate of decline of GFR, which is measured repeatedly over time in cohort participants.

The time to ESRD, defined by transplantation, dialysis, or a 50% decrease in GFR, is a secondary outcome measure. Measures of neurodevelopment, cognitive ability and growth, and cardiovascular disease risk factors are also assessed.

Inclusion criteria:

• For cohort 1, children between the ages of 1 and 16 years were enrolled if they had an estimated GFR (based on the Schwartz formula) between 30 and 90 ml/min/1.73m².
• For cohort 2, children between the ages of 1 and 16 years were enrolled if they had an estimated GFR (based on the Schwartz formula) between 45 and 90 ml/min/1.73m².

Exclusion criteria:

• Renal, other solid organ, bone marrow, or stem cell transplantation
• Dialysis treatment within the past three months
• Cancer diagnosis or HIV diagnosis/treatment within last 12 months
• Current pregnancy or pregnancy within past 12 months
• Inability to complete major data collection procedures
• 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
• History of structural heart disease
• Genetic syndromes involving the central nervous system (e.g., Down syndrome)
• History of severe to profound mental retardation (i.e., intelligence quotient (IQ) < 40, significant impairment in adaptive function and/or inability to independently execute self-care skills)

Results from the CKiD study have generated over 140 publications to date (https://statepi.jhsph.edu/ckid/publications/). Cross-sectional and longitudinal analysis of CKiD data has revealed valuable information that better defines the prevalence and impact of comorbid conditions and associated risk factors, including hypertension, LVH, dyslipidemia, anemia, poor growth, and abnormal neurocognitive development, that accompany CKD. To date, CKiD data has facilitated the development of more accurate estimating equations for GFR (https://ckid-gfrcalculator.shinyapps.io/eGFR/), which allows clinicians to monitor changes in kidney function of children over time. Longitudinal follow-up of the cohort is ongoing and will continue to provide insight on the progression of CKD (https://www.kidney.org/professionals/kdoqi/gfr_calculatorPedRisk).