EKFC Cystatin C

European Kidney Function Consortium

Cystatin C equation for adults, without sex or race terms

Biomarkers
Cystatin C
Validated for
18+ years
Inputs
Age, Cystatin C
Reports
mL/min/1.73 m²
Published
2023

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

Formula

eGFR=107.3×(ScysC/Q)α×{1if age≤400.990age−40if age>40\text{eGFR} = 107.3 \times (S_{cysC}/Q)^{\alpha} \times \begin{cases} 1 & \text{if age} \leq 40 \\ 0.990^{\text{age}-40} & \text{if age} > 40 \end{cases}

As text: eGFR = 107.3 × (SCysC/Q)^α × [0.990^(Age-40) if Age>40]; α = -0.322 if SCysC/Q < 1, α = -1.132 if SCysC/Q ≥ 1

Constants

SymbolMeaningValue
107.3Base coefficient
QQMedian serum cystatin C reference
Age ≤ 50: 0.83mg/L
Age > 50: 0.83 + 0.005 × (age − 50)mg/L
α\alphaExponent (depends on SCysC/Q ratio)
SCysC/Q < 1: −0.322
SCysC/Q ≥ 1: −1.132
Age factorAge correction applied only when age > 40
Age ≤ 40: 1 (no correction)
Age > 40: 0.990^(age − 40)
ScysCS_{cysC}Serum cystatin C (input)mg/L
AgePatient age (input)years

How it was developed

The EKFC creatinine equation was reused with rescaled cystatin C in place of rescaled creatinine, and the rescaling factor Q was estimated from cystatin C levels in 227,643 patients at Uppsala University Hospital, Sweden. The equation was validated against measured GFR in 12,832 adults: 11,231 from Europe, 1,093 from the United States and 508 from Africa.

Clinical notes

  • Q is the median cystatin C of men and women combined
  • Built on cystatin C assays standardized to ERM-DA471/IFCC
  • Averaged with EKFC creatinine for the EKFC combined equation

Limitations

  • Not validated in children
  • Not validated in Black American or Asian cohorts
  • Race- or sex-specific Q may be needed in some populations
  • Cystatin C may be altered by adiposity, smoking, thyroid disease, glucocorticoid excess, inflammation

References

  1. Pottel H, Björk J, Rule AD, et al. Cystatin C-Based Equation to Estimate GFR without the Inclusion of Race and Sex. N Engl J Med. 2023;388(4):333-343. doi:10.1056/NEJMoa2203769
  2. Delanaye P, Cavalier E, Pottel H, Stehlé T. New and old GFR equations: a European perspective. Clin Kidney J. 2023;16(9):1375-1383. doi:10.1093/ckj/sfad039

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