Estimate glomerular filtration rate in children using Schwartz, Counahan-Barratt, and CKiD formulas. Includes CKD staging and age-specific normal ranges.
Estimating glomerular filtration rate (GFR) in children requires formulas specifically designed for the pediatric population. Adult GFR equations like CKD-EPI and MDRD are not valid in children because creatinine generation relates to muscle mass, which changes dramatically with growth and development.
The Pediatric GFR Calculator supports the Updated Schwartz equation (2009), the classic Schwartz formula with age/sex-specific k-values, and the Counahan-Barratt equation. It also calculates GFR using the CKiD (Chronic Kidney Disease in Children) combined formula when cystatin C and BUN values are available.
This calculator maps estimated GFR to KDIGO chronic kidney disease (CKD) stages, provides age-specific normal GFR ranges, and calculates ancillary markers like BUN/Cr ratio. It is an essential tool for pediatric nephrologists, general pediatricians, and pharmacists dosing renally cleared medications in children. Check the example with realistic values before reporting. Use the steps shown to verify rounding and units. Cross-check this output using a known reference case. Use the example pattern when troubleshooting unexpected results.
Accurate GFR estimation is essential for detecting kidney disease, adjusting medication doses, and monitoring disease progression in children. Using adult formulas leads to systematic errors in pediatric patients.
This calculator provides multiple validated formulas, CKD staging, and visual tools that help clinicians quickly assess kidney function and determine the appropriate level of intervention or referral.
Updated Schwartz (2009): eGFR = 0.413 × Height (cm) / Serum Creatinine (mg/dL) Classic Schwartz: eGFR = k × Height (cm) / Serum Creatinine (mg/dL) k = 0.33 (preterm), 0.45 (term infant), 0.55 (child/adolescent F), 0.70 (adolescent M) Counahan-Barratt: eGFR = 0.43 × Height (cm) / Serum Creatinine (mg/dL)
Result: 90.9 mL/min/1.73m²
Using Updated Schwartz: 0.413 × 110 cm / 0.5 mg/dL = 90.9 mL/min/1.73m², which falls in the G1 (normal) CKD stage for an 8-year-old.
The original Schwartz formula (1976) used height and serum creatinine with an age/sex-specific constant (k) to estimate GFR. However, the k-values were derived using the Jaffé creatinine assay, which measures higher creatinine levels than modern enzymatic (IDMS-standardized) assays. Using the classic formula with current assays systematically overestimates GFR.
The Updated Schwartz equation (2009, also called the Bedside Schwartz) was derived from the CKiD cohort using IDMS-standardized creatinine. It uses a single k-value of 0.413 for all children aged 1-16, simplifying calculations while improving accuracy. This formula is now recommended as the first-line pediatric GFR estimate.
The Chronic Kidney Disease in Children (CKiD) study developed a combined formula incorporating creatinine, cystatin C, BUN, height, and sex. This multi-marker approach provides better accuracy than any single-marker formula, particularly in children with GFR 15-75 mL/min/1.73m².
Cystatin C adds independent information because its production is relatively constant regardless of diet, muscle mass, or age after infancy. Combining markers reduces the impact of individual assay variability and biological confounders.
Pediatric CKD management follows KDIGO staging (G1-G5), but interpretation must account for age-specific normal values. A GFR of 70 mL/min/1.73m² is normal for a 6-month-old but represents CKD stage 2 in a 5-year-old. Progressive decline in GFR over serial measurements is often more clinically significant than any single estimate.
The 2009 update was validated against iohexol-measured GFR using standardized (IDMS-traceable) creatinine assays, making it more accurate with modern lab methods. The classic formula overestimates GFR with current assays.
GFR matures with age. Term newborns have a GFR of ~40 mL/min/1.73m², which increases to adult levels (~90-130) by age 2. Premature infants start even lower.
Adult formulas (CKD-EPI) may be used in post-pubertal adolescents over age 18, but pediatric formulas remain preferable through age 18 as creatinine generation patterns differ from adults. Use this as a practical reminder before finalizing the result.
Cystatin C is a protein freely filtered by the glomerulus that is less affected by muscle mass than creatinine. Including it in the CKiD combined formula improves accuracy, especially in children with abnormal muscle mass.
Refer when eGFR is persistently below 60 mL/min/1.73m² (CKD stage 3+), when there is significant proteinuria, or when GFR is declining over serial measurements.
Height serves as a proxy for muscle mass (and thus creatinine generation) in pediatric formulas. Taller children generate more creatinine, so a higher creatinine in a tall child does not necessarily indicate worse kidney function.