EKFC Combined (Creatinine-Cystatin C)

Adult2023Recommended

Combined creatinine and cystatin C equation preferred in European guidance (EFLM/ERA)

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Calculate EKFC Cr-CysC

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For educational and clinical reference use. Interpret results in clinical context.

Formula

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

Formula constants

SymbolDescriptionValue
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}inputSerum creatininemg/dL
ScysCS_{cysC}inputSerum cystatin Cmg/L
AgeinputPatient ageyears

Required inputs

AgeSexCreatinineCystatin C

Validated age range

18 to 120 years

Limitations

  • Requires both creatinine and cystatin C measurements
  • Higher cost than single-biomarker equations
  • Requires standardized assays for both biomarkers
  • Cystatin C component validated in adults only (≥18 years)
  • KDIGO 2024 endorses CKD-EPI 2021 for global use; the EKFC preference reflects a European position (EFLM/ERA) rather than global consensus

Clinical notes

  • European-preferred equation when both biomarkers are available
  • Simple average of EKFC-Creatinine and EKFC-Cystatin C
  • Race-free equation
  • Validated in adult cohorts (≥18 years) — the cystatin C component has no pediatric validation
  • Close to 90% of results within ±30% of measured GFR
  • Recommended when both biomarkers are measured

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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