Chronic Kidney Disease in Children (CKiD) U25 eGFR Calculator
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Pediatric Kidney Function
CKiD U25 eGFR Calculator
Estimate glomerular filtration rate in children, adolescents, and young adults using the CKiD U25 creatinine based, cystatin C based, and combined equations.
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Clinical Information
CKiD U25 eGFR: Clinical Overview
The CKiD U25 equations provide an age and sex dependent approach to estimating glomerular filtration rate across childhood, adolescence, and young adulthood. The equations are designed for individuals from 1 to 25 years of age with mild to moderate chronic kidney disease.
About the CKiD U25 EquationsThe CKiD U25 equations were developed to provide a continuous approach to estimating kidney function from childhood through young adulthood. This helps avoid an abrupt transition to a different pediatric equation when a patient reaches 18 years of age.
The equations can be calculated using serum creatinine alone, cystatin C alone, or both biomarkers. When both biomarkers are available, the combined estimate is preferred because it generally provides better accuracy and precision than either single marker equation.
The equations do not use a race based coefficient. They are intended for clinical estimation of GFR and should not be considered a direct measurement of kidney function.
Equation OverviewCreatinine BasedeGFR = k × height ÷ serum creatinineHeight is expressed in meters. Serum creatinine is expressed in mg/dL.Cystatin C BasedeGFR = k × 1 ÷ cystatin CCystatin C is expressed in mg/L. Height is not required.CombinedCombined eGFR = (eGFRcr + eGFRcys) ÷ 2Calculated when both creatinine and cystatin C are available.Age and Sex Dependent CoefficientsThe creatinine based equation uses different coefficients according to age and sex. For males, the coefficient is 39.0 × 1.008 raised to the power of age − 12 from 1 to less than 12 years, 39.0 × 1.045 raised to the power of age − 12 from 12 to less than 18 years, and 50.8 from 18 to 25 years.
For females, the coefficient is 36.1 × 1.008 raised to the power of age − 12 from 1 to less than 12 years, 36.1 × 1.023 raised to the power of age − 12 from 12 to less than 18 years, and 41.4 from 18 to 25 years.
For the cystatin C equation, the male coefficient is 87.2 × 1.011 raised to the power of age − 15 from 1 to less than 15 years, 87.2 × 0.960 raised to the power of age − 15 from 15 to less than 18 years, and 77.1 from 18 to 25 years.
For females, the cystatin C coefficient is 79.9 × 1.004 raised to the power of age − 12 from 1 to less than 12 years, 79.9 × 0.974 raised to the power of age − 12 from 12 to less than 18 years, and 68.3 from 18 to 25 years.
Clinical InterpretationUse the Same Equation for Follow UpSerial eGFR values calculated using the same equation are generally more useful for assessing changes over time than comparing isolated values calculated using different equations.Creatinine and Muscle MassSerum creatinine is influenced by muscle mass and body composition. This should be considered when interpreting creatinine based estimates.Role of Cystatin CCystatin C provides complementary information and is less dependent on muscle mass, although it can also be influenced by factors unrelated to filtration.Age 18 to 25 YearsFor patients aged 18 to 25 years, CKiD U25 can be considered alongside an appropriate adult eGFR equation when clinically appropriate.Important Clinical NotesThe CKiD U25 eGFR is normalized to a body surface area of 1.73 m2. It is an estimated value and should not be interpreted as a direct measurement of GFR.
The CKiD U25 equations are intended for individuals aged 1 to 25 years with chronic kidney disease and should not be used as a stand alone diagnostic test for chronic kidney disease. Clinical history, laboratory findings, persistent evidence of kidney abnormality, and longitudinal assessment should be considered.
Serum creatinine should preferably be measured using an enzymatic method traceable to an IDMS reference measurement procedure. Cystatin C should preferably be measured using an IFCC standardized method.
Key References1 Pierce CB, Muñoz A, Ng DK, Warady BA, Furth SL, Schwartz GJ. Age and sex dependent clinical equations to estimate glomerular filtration rates in children and young adults with chronic kidney disease. Kidney International. 2021;99(4):948 to 956. doi:10.1016/j.kint.2020.10.0472 Ng DK, Furth SL, Warady BA, et al. Self reported race, serum creatinine, cystatin C, and GFR in children and young adults with pediatric kidney diseases: A report from the Chronic Kidney Disease in Children Study. American Journal of Kidney Diseases. 2022;80(2):174 to 185.e1.3 Nyman U, Björk J, Berg U, et al. The modified CKiD Study estimated GFR equations for children and young adults under 25 years of age: Performance in a European multicenter cohort. American Journal of Kidney Disease. 2022;80(6):807 to 810. doi:10.1053/j.ajkd.2022.02.0184 Ibrahim RB, Srivaths P, Tam E, Devaraj S. Utility of cystatin C based equation for the estimation of glomerular filtration rate in a pediatric population. The Journal of Applied Laboratory Medicine. 2024;9(4):803 to 808.5 Atkinson MA, Ng DK, Warady BA, Furth SL, Flynn JT. The CKiD study: overview and summary of findings related to kidney disease progression. Pediatric Nephrology. 2021;36(3):527 to 538.Primary source: National Institute of Diabetes and Digestive and Kidney Diseases. eGFR Equations for Children, Adolescents, and Young Adults. CKiD U25 equations.
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