99.1
mL/min/1.73m²
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99.1
mL/min/1.73m²
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The Schwartz Formula Calculator estimates glomerular filtration rate in pediatric patients using the updated bedside Schwartz equation. This is the recommended method for estimating GFR in children and adolescents aged 1-18 years, as adult equations such as CKD-EPI and MDRD are not validated for use in pediatric populations. The bedside Schwartz equation uses only height and serum creatinine, making it practical and easily applicable in clinical settings.
The updated bedside Schwartz equation is: eGFR = 0.413 x height (cm) / serum creatinine (mg/dL). This simplified version was developed from the Chronic Kidney Disease in Children (CKiD) cohort study and published in 2009. It replaced the original Schwartz formula from 1976, which used a variable constant k that differed by age and sex (k = 0.55 for children, 0.70 for adolescent males). The updated constant of 0.413 was calibrated for IDMS-standardized creatinine assays, which report lower creatinine values than the older Jaffe method used when the original formula was developed.
The rationale for including height in the equation is that in growing children, creatinine production is proportional to muscle mass, which correlates with height. Taller children produce more creatinine, so for a given serum creatinine level, a taller child has a higher GFR than a shorter child. This relationship is fundamentally different from adult equations, where age serves as the primary surrogate for muscle mass and creatinine generation. In children, age is a less reliable predictor because growth rates vary significantly.
Pediatric CKD is classified using the same GFR stages as adults (G1 through G5), but the interpretation and management differ in several important ways. Normal GFR in children increases with age, reaching adult levels by approximately 2 years of age. Neonates have a GFR of approximately 20-30 mL/min/1.73m2, which doubles by 2 weeks and reaches 60-80 by 6-12 months. Therefore, GFR values that would be abnormal in an adult may be normal in an infant. The Schwartz equation should not be used in neonates or infants under one year.
The CKiD study, from which the bedside Schwartz equation was derived, is the largest prospective cohort study of children with CKD in North America. It enrolled over 900 children and has generated extensive data on CKD progression, cardiovascular risk, neurocognitive outcomes, and growth in pediatric kidney disease. The equation was validated against measured GFR using iohexol clearance, with approximately 87% of estimates falling within 30% of measured GFR (P30).
Limitations of the bedside Schwartz equation include reduced accuracy in children with very low muscle mass (e.g., malnourished, wheelchair-bound), very high muscle mass, or unusual body composition. In these situations, cystatin C-based equations or the combined creatinine-cystatin C CKiD equation may provide more accurate estimates. Additionally, the equation assumes stable kidney function; in acute kidney injury, serum creatinine levels are rapidly changing and do not reflect steady-state conditions, making any creatinine-based equation unreliable.
The bedside Schwartz equation calculates eGFR = 0.413 x height (cm) / serum creatinine (mg/dL). The constant 0.413 was derived from the CKiD cohort and is calibrated for IDMS-standardized creatinine assays. Height serves as a surrogate for muscle mass and creatinine production in growing children. The result is expressed in mL/min/1.73m2.
Normal pediatric GFR is approximately 90-120 mL/min/1.73m2 after age 2 years. Values below 90 warrant investigation and monitoring. CKD staging follows the same GFR categories as adults: G1 (above 90), G2 (60-89), G3a (45-59), G3b (30-44), G4 (15-29), G5 (below 15). However, interpretation must account for normal developmental GFR changes in young children. Serial measurements are more informative than single values.
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Results
eGFR of 99.1 mL/min/1.73m2 is normal for an 8-year-old child. No evidence of kidney dysfunction.
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Results
eGFR of 29.9 indicates CKD Stage G4. This child needs close pediatric nephrology follow-up, growth monitoring, and preparation for possible renal replacement therapy.
The bedside Schwartz equation estimates pediatric GFR as eGFR = 0.413 x height (cm) / serum creatinine (mg/dL). It is the updated version of the original Schwartz formula, recalibrated for modern IDMS-standardized creatinine assays. It is recommended for children aged 1-18 years by KDIGO and the CKiD study group.
The original Schwartz constant (k = 0.55 for children) was derived using older Jaffe creatinine assays that reported higher values due to non-creatinine chromogens. Modern IDMS-standardized assays report lower creatinine values, requiring a recalibrated constant (0.413) to avoid overestimating GFR.
No. The Schwartz equation is designed for children aged 1-18 years. Adult GFR estimation should use CKD-EPI 2021 or Cockcroft-Gault. The relationship between height, creatinine, and GFR is different in adults who have completed growth.
The bedside Schwartz equation is not validated for infants under 1 year. Neonatal and infant GFR is physiologically low and rapidly changing. In this age group, measured GFR (using inulin or iohexol clearance) may be needed for accurate assessment.
The equation may be inaccurate in children with very low muscle mass (malnourished, wheelchair-bound, neuromuscular disease) or unusually high muscle mass (athletic teenagers). In these cases, cystatin C-based equations or the combined CKiD equation using both creatinine and cystatin C are preferred.
GFR increases rapidly after birth: approximately 20-30 mL/min/1.73m2 in neonates, doubling by 2 weeks, reaching 60-80 by 6-12 months, and approaching adult levels of 90-120 by age 2. After age 2, GFR remains relatively stable through childhood and adolescence.
The Chronic Kidney Disease in Children (CKiD) study is a large North American prospective cohort studying CKD progression and outcomes in children. It enrolled over 900 children from 54 sites and has produced the bedside Schwartz equation along with extensive data on pediatric CKD management, growth, cardiovascular risk, and neurocognition.
Approximately 87% of estimates fall within 30% of measured GFR (P30), and 45% within 10% (P10). Accuracy is best in the GFR range of 15-75 mL/min/1.73m2, which is the range most clinically relevant for CKD management decisions in children.
Standing height (stadiometry) is used for children who can stand. Recumbent length is used for infants and children who cannot stand. Recumbent length is typically 0.5-1 cm longer than standing height. Consistency in measurement method is important for serial GFR monitoring.
The Schwartz equation uses height, not weight, so obesity has less direct impact than on adult equations. However, obese children may have higher muscle mass for their height, potentially affecting creatinine generation. The equation has not been extensively validated specifically in obese pediatric populations.
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