Interpretation
| Result | Meaning |
|---|---|
| ≥ 90 | G1 |
| 60–89 | G2 |
| 45–59 | G3a |
| 30–44 | G3b |
| 15–29 | G4 |
| < 15 | G5 |
Formula
eGFR(Cr) = K × height (m) ÷ SCr (mg/dL). Males: K = 39.0 × 1.008^(age−12) (age < 12), 39.0 × 1.045^(age−12) (12–<18), 50.8 (≥18). Females: 36.1 × 1.008^(age−12), 36.1 × 1.023^(age−12), 41.4. eGFR(CysC) = K ÷ CysC (mg/L). Males: 87.2 × 1.011^(age−15) (< 15), 87.2 × 0.960^(age−15) (15–<18), 77.1 (≥18). Females: 79.9 × 1.004^(age−12) (< 12), 79.9 × 0.974^(age−12) (12–<18), 68.3 (≥18). Combined = average of the two.
Clinical pearls
- Derived in children and young adults with CKD (CKiD cohort, median mGFR ≈ 48); accuracy in children with normal kidney function is not established.
- Requires IDMS-traceable enzymatic creatinine and IFCC-standardized cystatin C. Not valid in AKI (non-steady state).
- Cystatin C helps when muscle mass is atypical for height (e.g. neuromuscular disease, amputation, malnutrition).
Examples
ckid u25 10 yo boy height 140 cm creatinine 0.6pediatric egfr 15F 160 cm cr 0.8 cystatin 1.2u25 egfr 20 year old woman, 165 cm, creatinine 88 umol/L
FAQ
How is CKiD U25 different from the bedside Schwartz equation?
Bedside Schwartz uses a single constant (0.413 × height cm / SCr); U25 uses sex- and age-specific K values, reducing bias in young children and young adults up to age 25.
Should I use creatinine or cystatin C?
Either works; when both are available the average of the two U25 estimates is more accurate than either alone.