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 that account for growth, body size, and changing creatinine production. Adult equations such as CKD-EPI and MDRD are not designed for that setting.
The Pediatric GFR Calculator includes the Updated Schwartz equation, the classic Schwartz formula, the Counahan-Barratt equation, and the CKiD combined formula when cystatin C and BUN are available. That gives you a quick way to compare the common pediatric estimates side by side.
It also maps the result to KDIGO CKD stages and shows age-aware normal ranges, which makes the number easier to interpret in clinical context.
Pediatric kidney function is hard to estimate from creatinine alone because body size and muscle mass change quickly with age. The calculator makes it easier to compare the most common formulas without doing each calculation by hand.
Seeing the estimated GFR alongside CKD staging and an age-aware reference range helps put the result into a more useful clinical frame.
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. It is now one of the most commonly used pediatric creatinine-based eGFR starting points.
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.
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This worksheet applies the bedside Schwartz and related pediatric kidney-function equations to estimate GFR from creatinine and growth data. It is a comparison aid, not a substitute for full nephrology review or trend interpretation.
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 may be reasonable in some post-pubertal adolescents, but pediatric equations remain the safer default through childhood and adolescence because creatinine generation and body composition are still changing.
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.