Pediatric eGFR: Bedside Schwartz, CKiD U25 and Interpretation

Kidney function in children needs age-appropriate assessment. The adult CKD-EPI 2021 equation is not intended for children under 18. Our pediatric calculator implements the 2009 CKiD bedside equation, often called bedside Schwartz, as a simplified educational estimate.

It is one pediatric method, not a replacement for a pediatrician or a claim that every child should use the same formula.

The bedside equation and unit check

eGFR = 0.413 × height in cm / serum creatinine in mg/dL

The result is in mL/min/1.73 m². Height must be in centimeters for the 0.413 coefficient. Creatinine in µmol/L must first be divided by 88.4. Using meters with 0.413 or entering µmol/L as mg/dL creates a large error.

NIDDK's pediatric equations reference describes the equation as developed mainly from children aged 8–15 with mild-to-moderate CKD, and used for quick estimates in routine care. Its study population should not be mistaken for validation in every child, especially newborns or those with rapidly changing kidney function.

A worked example

A child does not receive a diagnosis from this result alone. The clinician considers age, growth, blood pressure, urine tests, prior results, and the reason for testing.

Why CKiD U25 matters

NIDDK also presents the CKiD U25 equations for children and young adults aged 1–25. They use age- and sex-dependent coefficients with creatinine, cystatin C, or both. They can support follow-up across the transition to adult care; for ages 18–25, comparing an appropriate pediatric/young-adult estimate with an adult estimate may be useful.

Our bedside tool does not calculate CKiD U25. Do not label its output as a U25 result or assume it equals a specialist laboratory's preferred estimate. Ask the care team which formula is appropriate and why.

Where a simple estimate can mislead

Very low muscle mass, unusual body composition, acute illness, and assay differences can affect serum creatinine. Enzymatic creatinine assays are preferable in children when available because low concentrations are more vulnerable to interference with some methods. Kidney function in newborns changes with maturation and requires a separate approach.

A formula also assumes the blood marker is sufficiently stable. During acute illness, the clinician evaluates changing creatinine and urine output rather than relying on one calculated eGFR.

Prepare for a pediatric appointment

Bring the laboratory report, its unit, a recent measured height, dates of previous tests, and a medication list. Useful questions include:

1. Which equation and creatinine assay were used?
2. Is the estimate appropriate for this age and condition?
3. Are urine albumin, blood in urine, blood pressure, growth or imaging abnormal?
4. Would cystatin C or another method clarify a conflicting result?
5. When should tests be repeated, and which symptoms need urgent assessment?

Do not use an adult diet target or medicine-dose rule for a child. The pediatric care team considers growth and nutrition as well as kidney function. The adult formula guide explains why adult inputs alone cannot solve these pediatric questions.