CKD-EPI GFR Calculator (2021)

Equation Type

Uses only serum creatinine for GFR estimation

Age

Serum Creatinine

Gender

Disclaimer: This calculator provides an estimate of glomerular filtration rate using the 2021 CKD-EPI equations (race-neutral). It should not replace professional medical advice. Consult with a healthcare provider for proper kidney function assessment.

2021 CKD-EPI Formulas Explained

2021 CKD-EPI Creatinine Equation

eGFR = 142 × min(Scr/κ, 1)^α × max(Scr/κ, 1)^(-1.200) × 0.9938^Age × 1.012 [if female]

Where:

• Scr = standardized serum creatinine in mg/dL

• κ = 0.7 for females or 0.9 for males

• α = -0.241 for females or -0.302 for males

• min(Scr/κ, 1) = the minimum of Scr/κ or 1

• max(Scr/κ, 1) = the maximum of Scr/κ or 1

• Age = age in years

2021 CKD-EPI Creatinine-Cystatin C Equation

eGFR = 135 × min(Scr/κ, 1)^α × max(Scr/κ, 1)^(-0.544) × min(Scys/0.8, 1)^(-0.323) × max(Scys/0.8, 1)^(-0.778) × 0.9961^Age × 0.963 [if female]

Where:

• Scr = standardized serum creatinine in mg/dL

• Scys = standardized serum cystatin C in mg/L

• κ = 0.7 for females or 0.9 for males

• α = -0.219 for females or -0.144 for males

• min(Scr/κ, 1) = the minimum of Scr/κ or 1

• max(Scr/κ, 1) = the maximum of Scr/κ or 1

• min(Scys/0.8, 1) = the minimum of Scys/0.8 or 1

• max(Scys/0.8, 1) = the maximum of Scys/0.8 or 1

• Age = age in years

Key Changes in 2021 Version

• Race-neutral: Removed race coefficient for more equitable care

• Updated coefficients: More accurate across all populations

• Simplified calculation: Single equation for all patients

• Better precision: Improved accuracy at higher GFR levels

• Combined equation: Creatinine-cystatin C equation for improved accuracy

Step-by-Step Calculation

Gather required values

Age in years, serum creatinine in mg/dL, gender, and optionally cystatin C in mg/L

Example: 65 years, 1.2 mg/dL, Male, 1.1 mg/L (if using combined equation)

Determine coefficients

Set κ and α based on gender and equation type

For creatinine equation: Male → κ=0.9, α=-0.302

For combined equation: Male → κ=0.9, α=-0.144

Calculate min and max values

Calculate Scr/κ, then min(Scr/κ, 1) and max(Scr/κ, 1)

Example: 1.2/0.9 = 1.33, min=1, max=1.33

Apply the appropriate CKD-EPI formula

Use creatinine-only or combined equation based on available data

Creatinine equation: 142 × min^α × max^(-1.200) × 0.9938^Age

Combined equation: 135 × min^α × max^(-0.544) × minCys^(-0.323) × maxCys^(-0.778) × 0.9961^Age

Apply gender adjustment

For females, multiply by 1.012 (creatinine) or 0.963 (combined)

Example: 78.4 × 1.012 = 79.3 mL/min/1.73m² (if female, creatinine equation)

CKD Stages Classification

Stage 1

≥ 90 mL/min/1.73m²

Stage 2

60-89 mL/min/1.73m²

Stage 3a

45-59 mL/min/1.73m²

Stage 3b

30-44 mL/min/1.73m²

Stage 4

15-29 mL/min/1.73m²

Stage 5

< 15 mL/min/1.73m²

2021 CKD-EPI Advantages

• Race-neutral: Promotes health equity by removing race-based adjustments
• More accurate: Better performance than previous versions across all populations
• Simplified: Single equation for all patients regardless of race
• Updated coefficients: Based on more diverse and recent data
• Recommended standard: Endorsed by NKF and ASN for clinical use
• Better precision: Improved accuracy at higher GFR levels
• Combined equation: Creatinine-cystatin C equation for enhanced accuracy

Important Limitations

• Not accurate in patients with rapidly changing kidney function
• May be less reliable in patients with muscle wasting or amputation
• Should not be used for drug dosing in critically ill patients
• Consider measured GFR for important clinical decisions
• Requires standardized creatinine and cystatin C measurements (IDMS-traceable)
• Age and gender are important factors in the calculation
• Cystatin C may not be available in all laboratories

The CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration) equations are widely used formulas for estimating the glomerular filtration rate (eGFR), a critical indicator of kidney function. Introduced in 2009 and refined in 2012 and 2021, the CKD-EPI equations were developed to overcome limitations of the earlier MDRD (Modification of Diet in Renal Disease) equation, which often underestimated GFR at higher values. By incorporating larger and more diverse patient cohorts, CKD-EPI equations provide more accurate and reliable GFR estimates across a broader spectrum of kidney function.

Estimating GFR is essential in diagnosing, staging, and monitoring chronic kidney disease (CKD). Direct GFR measurement using inulin or radioisotopes is rarely performed in routine practice due to cost and complexity. Instead, equations based on serum biomarkers (like creatinine and cystatin C), age, and sex are used to provide practical estimates. CKD-EPI is currently the preferred equation recommended by leading nephrology societies worldwide.

Types of CKD-EPI Equations

Several versions of the CKD-EPI equation exist, tailored to different biomarkers:

CKD-EPI Creatinine Equation (2009): Uses serum creatinine, age, sex, and race (though the race factor was later removed in 2021).
CKD-EPI Cystatin C Equation (2012): Uses serum cystatin C, a filtration marker less influenced by muscle mass.
CKD-EPI Creatinine–Cystatin C Equation (2012): Combines both markers, improving accuracy across populations.
CKD-EPI Race-Free Equation (2021): A revision that eliminates the race variable to address concerns of health equity and bias while maintaining accuracy.

CKD-EPI Creatinine Equation (2009)

The original CKD-EPI creatinine-based equation is:

eGFR = 141 × min(Scr/κ, 1)^α × max(Scr/κ, 1)^−1.209 × (0.993)^Age × (1.018 if female) × (1.159 if Black)

Where: – Scr = serum creatinine (mg/dL) – κ = 0.7 for females, 0.9 for males – α = −0.329 for females, −0.411 for males – min = minimum of (Scr/κ) or 1 – max = maximum of (Scr/κ) or 1

Normal Ranges / Interpretation

CKD-EPI eGFR values are expressed in mL/min/1.73 m² and are interpreted for staging CKD as follows:

eGFR (mL/min/1.73 m²)	CKD Stage	Clinical Meaning
≥ 90	Stage 1	Normal or high GFR; CKD only if proteinuria or structural damage present
60 – 89	Stage 2	Mild decrease; requires other evidence of kidney damage
45 – 59	Stage 3a	Mild-to-moderate impairment
30 – 44	Stage 3b	Moderate-to-severe impairment
15 – 29	Stage 4	Severe impairment; prepare for renal replacement therapy
< 15	Stage 5	Kidney failure; dialysis or transplant indicated

Clinical Significance

CKD-EPI equations have become the gold standard for GFR estimation due to their clinical advantages:

Improved accuracy: Provides more reliable results than MDRD, particularly when GFR is near-normal (> 60 mL/min/1.73 m²).
CKD diagnosis and staging: Ensures accurate classification of patients across CKD stages, reducing overdiagnosis.
Risk prediction: eGFR correlates with outcomes such as cardiovascular disease, hospitalization, and mortality.
Treatment planning: Guides blood pressure control, glycemic targets, medication selection, and preparation for renal replacement therapy.
Research and public health: Used globally in epidemiological studies to estimate CKD prevalence and burden.

Indications for Use

CKD-EPI equations should be applied in:

Routine kidney function assessment during annual health checks.
Screening patients with risk factors (diabetes, hypertension, cardiovascular disease).
Diagnosing and staging chronic kidney disease.
Monitoring disease progression in CKD patients.
Population studies for estimating CKD prevalence.

Limitations

Despite their advantages, CKD-EPI equations are not without limitations:

Serum creatinine variability: Creatinine is influenced by muscle mass, diet, and medications, which may affect accuracy in frail or muscular patients.
Special populations: Less accurate in children, pregnant women, critically ill patients, and certain ethnic groups not well represented in derivation cohorts.
Cystatin C considerations: While less dependent on muscle mass, cystatin C can be influenced by inflammation, thyroid disease, or corticosteroid use.
Assay standardization: Results depend on accurate, standardized laboratory measurements of creatinine and cystatin C.

CalcMD.

CKD-EPI Equations for Glomerular Filtration Rate

Learn about the CKD-EPI equations for estimating glomerular filtration rate (GFR). Explore formulas, normal ranges, clinical significance, indications, and limitations compared to MDRD.