EKFC Creatinine-Cystatin C

European Kidney Function Consortium

Combined creatinine and cystatin C equation for adults

Biomarkers
Creatinine + cystatin C
Validated for
18+ years
Inputs
Age, Sex, Creatinine, 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

eGFRcombined=eGFREKFC-Cr+eGFREKFC-CysC2\text{eGFR}_{\text{combined}} = \frac{\text{eGFR}_{\text{EKFC-Cr}} + \text{eGFR}_{\text{EKFC-CysC}}}{2}

As text: eGFR = Mean of EKFC-Creatinine and EKFC-Cystatin C equations

Constants

SymbolMeaningValue
eGFREKFC-Cr\text{eGFR}_{\text{EKFC-Cr}}EKFC Creatinine result (see EKFC Creatinine equation)mL/min/1.73m²
eGFREKFC-CysC\text{eGFR}_{\text{EKFC-CysC}}EKFC Cystatin C result (see EKFC Cystatin C equation)mL/min/1.73m²
Q (creatinine)Median serum creatinine of healthy persons (rescaling factor)
Female (>25 y): 0.70 (62 µmol/L)mg/dL
Male (>25 y): 0.90 (80 µmol/L)mg/dL
2–25 y: ln(Q) polynomial in age (Pottel 2021, Figure 1)mg/dL
Q (cystatin C)Median serum cystatin C reference
Age ≤ 50: 0.83mg/L
Age > 50: 0.83 + 0.005 × (age − 50)mg/L
ScrS_{cr}Serum creatinine (input)mg/dL
ScysCS_{cysC}Serum cystatin C (input)mg/L
AgePatient age (input)years

How it was developed

The cystatin C rescaling factor (Q) was estimated from 227,643 White patients at Uppsala University Hospital, Sweden. The combined equation, the arithmetic mean of the EKFC creatinine and EKFC cystatin C estimates, was evaluated in 12,832 adults from Europe (11,231), the United States (1,093) and Africa (508), against GFR measured by plasma or urinary clearance of exogenous filtration markers.

Clinical notes

  • Averages the EKFC creatinine and EKFC cystatin C estimates
  • Built on IDMS-calibrated creatinine and ERM-DA471/IFCC-standardized cystatin C
  • Listed among validated GFR equations in KDIGO 2024

Limitations

  • Validation lacked cohorts of children, Asian patients and US Black patients
  • Creatinine Q values are for White Europeans; Black-specific values not applied
  • Single cystatin C Q may need race- or sex-specific values in some populations

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. Pottel H, Björk J, Courbebaisse M, et al. Development and validation of a modified full age spectrum creatinine-based equation to estimate glomerular filtration rate. Ann Intern Med. 2021;174(2):183-191. doi:10.7326/M20-4366
  3. 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
  4. Delanaye P, Schaeffner E, Cozzolino M, Langlois M, Plebani M, Ozben T, Cavalier E. The new, race-free, Chronic Kidney Disease Epidemiology Consortium (CKD-EPI) equation to estimate glomerular filtration rate: is it applicable in Europe? A position statement by the European Federation of Clinical Chemistry and Laboratory Medicine (EFLM). Clin Chem Lab Med. 2023;61(1):44-47. doi:10.1515/cclm-2022-0928

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