The Schwartz formula is the standard bedside estimate of kidney function in children. Because children vary so widely in size, it scales glomerular filtration rate directly with height rather than relying on adult equations that assume a fixed body habitus.
How it works
The updated 2009 bedside equation is deliberately simple:
eGFR = 0.413 × height (cm) / serum creatinine (mg/dL)The constant of 0.413 applies to all children aged 1 to 17 when creatinine is measured by a modern IDMS-traceable enzymatic assay. If your laboratory reports creatinine in micromol per litre, divide by 88.4 to convert to mg/dL first; the tool does this automatically and shows the converted value. The result is expressed in mL/min per 1.73 m², the standard normalisation for GFR in paediatrics.
Why the constant changed from the original Schwartz formula
The original 1976 Schwartz formula used age- and sex-specific constants (0.33 for premature infants, 0.45 for term infants, 0.55 for children and adolescent girls, 0.70 for adolescent boys). These were derived from data collected when creatinine was measured with the Jaffe colorimetric method, which overestimates creatinine in plasma due to non-creatinine chromogens, particularly in healthy children whose creatinine is low.
When IDMS-traceable enzymatic assays became the standard — producing more accurate and lower creatinine values — the old constants systematically overestimated GFR. The 2009 CKiD study derived the new constant of 0.413 against iohexol-measured GFR using enzymatic creatinine, collapsing the age- and sex-specific constants into a single value that fits the modern measurement environment.
If you are working with a laboratory that still uses Jaffe method creatinine (less common now), the 2009 bedside constant is not the right one. Confirm your laboratory’s creatinine method before applying the equation.
CKD staging in children
The result maps to the same KDIGO GFR categories used in adults:
| Stage | eGFR (mL/min per 1.73 m²) | Description |
|---|---|---|
| G1 | ≥ 90 | Normal or high (with other markers of kidney damage) |
| G2 | 60–89 | Mildly decreased |
| G3a | 45–59 | Mildly to moderately decreased |
| G3b | 30–44 | Moderately to severely decreased |
| G4 | 15–29 | Severely decreased |
| G5 | < 15 | Kidney failure |
In paediatric nephrology, CKD staging guides the intensity of monitoring, dietary management, and the timing of preparation for renal replacement therapy planning. However, a single eGFR estimate is insufficient for staging — CKD requires evidence of kidney damage or reduced eGFR persisting for more than three months.
When to reach for measured rather than estimated GFR
Creatinine-based estimates work well in stable CKD but are less reliable in several situations:
- Acute kidney injury — creatinine rises later than actual GFR falls, so eGFR lags. Do not use Schwartz to track rapidly changing function.
- Severe malnutrition or muscle wasting — very low muscle mass produces unusually low creatinine, artificially inflating the eGFR estimate.
- Unusual height-to-muscle-mass relationships — the formula assumes typical growth patterns; children with disproportionate limb or trunk growth (some skeletal dysplasias, spastic cerebral palsy) may not fit the model.
- Before high-stakes decisions — for transplant work-up, chemotherapy dosing, or major dose adjustments of renally cleared drugs, a measured GFR (cystatin C-based eGFR or iohexol/inulin clearance) provides more accuracy than any creatinine-based estimate.
Interpretation and notes
The estimate is validated for chronic kidney disease in children from about one year of age and is not intended for neonates. Always review results alongside clinical context, urine findings, imaging, and trend over time rather than as a standalone value.