Serum eGFR (estimated Glomerular Filtration Rate) is commonly calculated using the CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration) formula, which estimates kidney function based on serum creatinine, age, and sex.
CKD-EPI 2021 Creatinine Equation
The most widely used formula is:eGFR=142×min(SCrκ,1)α×max(SCrκ,1)−1.200×(0.9938)Age×1.012 [if female]eGFR=142×min(κSCr,1)α×max(κSCr,1)−1.200×(0.9938)Age×1.012 [if female]
Where:
- SCr = serum creatinine (mg/dL)
- κ = 0.7 (females), 0.9 (males)
- α = -0.241 (females), -0.302 (males)
- Age in years
- The last multiplier (1.012) is only for females.
Other eGFR Formulas
Additional formulas use cystatin C alone or combine creatinine and cystatin C, especially if precise assessment is needed for clinical decisions.
- 2021 CKD-EPI creatinine-cystatin C equation
- 2012 CKD-EPI cystatin C equation
These formulas incorporate more biomarkers for improved accuracy, but the most routine calculation is with serum creatinine.
WHICH EQUATION IS PREFERRED?
Serum eGFR is best calculated using the CKD-EPI equation, integrating serum creatinine, age, and sex to yield an estimate of kidney function vital for disease staging and medication dosing.
IT IS IMPORTANT TO NOTE:
Caution should be applied when interpreting eGFR across different age groups. The standard adult eGFR formulas, like CKD-EPI, are not valid for children under 18—pediatric-specific formulas such as the Schwartz equation should be used for this population.
Additionally, in older adults, eGFR naturally declines with age even in the absence of kidney disease, which means a single fixed cutoff for CKD diagnosis may lead to overdiagnosis and unnecessary interventions in the elderly.
REFERENCES AND RESOURCES:
- National Kidney Foundation, CKD-EPI Creatinine Equation (2021): https://www.kidney.org/ckd-epi-creatinine-equation-2021
- NIDDK, eGFR Equations for Adults: https://www.niddk.nih.gov/research-funding/research-programs/kidney-clinical-research-epidemiology/laboratory/glomerular-filtration-rate-equations/adults
- Medscape eGFR calculator (CKD-EPI 2021): https://reference.medscape.com/calculator/251/egfr-using-ckd-epi-2021-update
- Original CKD-EPI Equation publication (2009): https://pmc.ncbi.nlm.nih.gov/articles/PMC2763564/