CKiD U25 Cystatin C

Chronic Kidney Disease in Children study

Cystatin C equation for children and young adults with CKD

Biomarkers
Cystatin C
Validated for
1–25 years
Inputs
Age, Sex, Cystatin C
Reports
mL/min/1.73 m²
Published
2021

The eGFR guide explains which equation the calculator suggests and indexed and absolute GFR.

Formula

eGFR=κ×1CysC\text{eGFR} = \kappa \times \frac{1}{\text{CysC}}

As text: eGFR = κ × (1/cysC) where κ varies by sex and age

Constants

SymbolMeaningValue
κ\kappaAge- and sex-dependent coefficient (Female)
Age 1 to <12: 79.9 × 1.004^(age − 12)
Age 12 to ≤15: 79.9 × 0.974^(age − 12)
Age >15 to <18: 79.9 × 0.974^(age − 12)
Age 18–25: 68.3
κ\kappaAge- and sex-dependent coefficient (Male)
Age 1 to <12: 87.2 × 1.011^(age − 15)
Age 12 to ≤15: 87.2 × 1.011^(age − 15)
Age >15 to <18: 87.2 × 0.960^(age − 15)
Age 18–25: 77.1
CysCSerum cystatin C (input)mg/L

How it was developed

Developed alongside the U25 creatinine equation, in the same CKiD Study cohort of children and young adults with mild to moderate CKD. Training used the same 618 participants (cystatin C, calibrated to IFCC standards, was missing for 81 of their 1,764 visits), with GFR measured by plasma iohexol disappearance; 843 observations from 304 other participants formed the internal validation set.

Clinical notes

  • Does not use height, unlike the U25 creatinine equation
  • Paper averages it with the U25 creatinine estimate when both are available
  • Developed with nephelometric cystatin C from one central laboratory

Limitations

  • Not developed or validated in people without CKD, or for screening
  • Validated only internally, in a subset of CKiD data
  • Developed only from visits before end-stage kidney disease

References

  1. Pierce CB, Muñoz A, Ng DK, Warady BA, Furth SL, Schwartz GJ. Age- and sex-dependent clinical equations to estimate glomerular filtration rates in children and young adults with chronic kidney disease. Kidney Int. 2021;99(4):948-956. doi:10.1016/j.kint.2020.10.047

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