eGFR Equations for Children, Adolescents, & Young Adults
The following estimated glomerular filtration rate (eGFR) equations are available for use in children, adolescents, and young adults
- Chronic Kidney Disease in Children under (age) 25 (CKiD U25) equations
- Neonatal eGFR equation
- European Kidney Function Consortium (EKFC) equations
- 2009 Creatinine-based CKiD “bedside” equation
Equations
NIDDK calculates eGFR using creatinine determinations that are traceable to an isotope dilution mass spectrometry (IDMS) reference measurement procedure and cystatin C determinations that are traceable to ERM-DA471_IFCC HUMAN SERUM (cystatin C) certified reference material.
CKiD U25 Equations
The CKiD U25 equations are for use in individuals ages 1 to 25, with mild-to-moderate chronic kidney disease (CKD).1 These equations offer superior estimation of CKD-range GFR across the pediatric and young adult age spectrum and are more appropriate for clinical decision making for adults in the age 18 to 25 interval than the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equations.2 The U25 equations can monitor kidney function and disease progression longitudinally, without the “jumps” in eGFR that may occur when transitioning from pediatric-specific equations to adult equations at age 18. The U25 equations demonstrate minimal, nonsignificant bias in both pediatric and young adult CKD populations, and they don’t require race-based modifiers.1,2
The CKiD U25 equations estimate GFR using either serum creatinine or cystatin C alone, or the average of the serum creatinine and cystatin C estimates. When both filtration markers are available the averaged equation is preferred, as it provides a more accurate and precise estimate of GFR than either single-marker estimation.1,2
CKiD U25 Creatinine Equation
In addition to demonstrating minimal, nonsignificant bias in pediatric and young adult populations with CKD, the CKiD U25 creatinine equation (U25 eGFRcr) has been shown to provide valid estimates of GFR in pediatric and young adult populations with eGFR ≥ 75 ml/min/1.73m2, as demonstrated in a cohort of healthy European children and young adults.3
eGFR = κ × (ht/SCr)
where:
- eGFR = estimated GFR in mL/min/1.73 m2
- κ = sex- and age-dependent κ values (see Table 1)
- SCr = enzymatically assayed (recommended) in mg/dL
- ht = height in meters
Table 1. Sex- and age-dependent values of K for CKiD U25 eGFRcr
| Age, years | Female | Male |
|---|---|---|
| 1 to <12 | 36.1 × 1.008(Age–12) | 39.0 × 1.008(Age–12) |
| 12 to <18 | 36.1 × 1.023(Age–12) | 39.0 × 1.045(Age–12) |
| 18 to 25 | 41.4 | 50.8 |
GFR conversion factors
- GFR mL/min/1.73 m2 to mL/s/1.73 m2, multiply by 0.0167
- serum creatinine µmol/L to mg/dL, divide by 88.4
CKiD U25 Cystatin C Equation
The CKiD U25 cystatin C equation (U25 eGFRcys) demonstrated minimal, nonsignificant bias in pediatric and young adult populations with CKD,1 but the equation may not be appropriate for screening of asymptomatic patients for CKD in this age range. The U25 eGFRcys equation significantly underestimated measured GFR in a cohort of healthy European children and young adults.3
eGFR = κ × (1/cysC)
where:
- eGFR = estimated GFR in mL/min/1.73 m2
- κ = sex- and age-dependent κ values (see Table 2)
- cysC = nephelometrically assayed (recommended), International Federation of Clinical Chemistry (IFCC)-standardized cystatin C in mg/L
Table 2. Sex- and age-dependent values of K for CKiD U25 eGFRcys
| Age, years | Female | Male |
|---|---|---|
| 1 to <12 | 79.9 × 1.004(Age–12) | 87.2 × 1.011(Age–15) |
| 12 to 15 | 79.9 × 0.974(Age–12) | 87.2 × 1.011(Age–15) |
| 15 to <18 | 79.9 × 0.974(Age–12) | 87.2 × 0.960(Age–15) |
| 18 to 25 | 68.3 | 77.1 |
GFR conversion factors
- GFR mL/min/1.73 m2 to mL/s/1.73 m2, multiply by 0.0167
- cystatin C does not require unit conversion
CKiD U25 Creatinine-cystatin C Equation
The CKiD U25 creatinine-cystatin C equation (U25 eGFRcr-cys) provides a more accurate estimate than using either serum creatine or cystatin C alone in CKD.1,2
eGFR = (U25 eGFRcr + U25 eGFRcys)/2
where:
- eGFR = estimated GFR in mL/min/1.73 m2
- U25 eGFRcr = serum creatinine-based estimated GFR
- U25 eGFRcys = cystatin C-based estimated GFR
Neonatal eGFR Equation
The neonatal eGFR equation is designed to help identify altered GFR in term-born infants up to 4 weeks of age.4
eGFR = 0.31 x ht/SCr
where:
- eGFR = estimated GFR in mL/min/1.73 m2
- SCr = enzymatically assayed (recommended), serum creatinine in mg/dL standardized to an isotope dilution mass spectrometry reference measurement procedure
- ht = height in centimeters
GFR conversion factors
- serum creatinine µmol/L to mg/dL, divide by 88.4
EKFC Equations
The EKFC equations provide estimates of GFR across a wide age spectrum—from children older than 2 years to adults.5,6 As full age spectrum equations, the EKFC equations can be used continuously for patients transitioning from pediatric to adult care.
EKFC Creatinine Equation
The EKFC creatinine equation (EKFC eGFRcr) appears to perform well in individuals with normal and higher range GFRs. Please note, the EKFC eGFRcr equation was developed in a population of White, European children and adults and has not yet been fully validated in diverse populations. Additionally, the EKFC eGFRcr equation is based on rescaling a “Q value” for creatinine, which includes race and/or ancestry-based adjustment for different populations. Q factors have not been established for the United States overall or for regional populations. Accordingly, the equation does not meet recommendations for race-free equations.
Learn more about the EKFC creatinine equation in Development and Validation of a Modified Full Age Spectrum Creatine-based Equation to Estimate Glomerular Filtration Rate.5
EKFC Cystatin C Equation
While the EKFC cystatin C equation (EKFC eGFRcys) was developed primarily in a population of White, European children and adults, a small number of individuals of African ancestry were included in the derivation and validation populations. An advantage of the EKFC eGFRcys equation over the EKFC eGFRcr equation is that it is not affected by race and, accordingly, can provide an alternative race-free eGFR estimation.
Learn more about the EKFC cystatin C equation in Cystatin C-Based Equation to Estimate GFR without the Inclusion of Race and Sex.6
Overall, it appears that the EKFC eGFRcys equation may have similar performance to the CKD-EPI eGFRcys equation, although each equation may perform better in different subgroups, such as those with renal insufficiency and those with normal kidney function, and in certain age subgroups. Further validation in various populations and subgroups may provide additional insight.
EKFC Creatinine-cystatin C Equation
The EKFC creatinine-cystatin C equation (EKFC eGFRcr-cys), which averages the EKFC eGFRcr and EKFC eGFRcys equations, provides a more accurate estimate than using either serum creatine or cystatin C alone.6
2009 Creatinine-based CKiD “Bedside” Equation
The CKiD “bedside” equation was developed using data primarily from children ages 8 to 15 with mild-to-moderate CKD and is reserved for quick, urgent estimates during routine clinical care of children.7 The CKiD “bedside” equation estimates GFR using height and serum creatinine. The equation can be calculated in conventional or SI units.
Conventional Units
eGFR = 41.3 × (ht/SCr)
where:
- eGFR = estimated GFR in mL/min/1.73 m2
- SCr = standardized serum creatinine in mg/dL
- ht = height in meters
SI Units
eGFR = 36.5 × (ht/SCr)
where:
- eGFR = estimated GFR in mL/min/1.73 m2
- SCr = standardized serum creatinine in µmol/L
- ht = height in centimeters
Serum Creatinine Measurement Considerations for Children, Adolescents, and Young Adults
Enzymatic methods of serum creatinine determination are superior and should be used to measure creatinine in children whenever possible. The alkaline picrate (Jaffe) method is more susceptible to interfering substances, including endogenous substances such as glucose and protein, which can affect the accuracy of the creatinine measurement. The lower serum creatinine concentration and lower serum total protein concentration in children can further magnify the risk of interference and inaccuracies when the alkaline picrate (Jaffe) method is used.