Estimated Glomerular Filtration Rate
eGFR estimates kidney function from creatinine (and optionally cystatin C). CKD-EPI 2021 is the preferred equation. CKD staging guides management and referral.
Why This Health Metric Matters
Why: Kidney function affects drug dosing, contrast decisions, and long-term prognosis. Early CKD detection enables intervention.
How: Equations use creatinine, age, sex. CKD-EPI 2021 is most accurate. Cystatin C adds value when creatinine is unreliable.
- ●CKD-EPI 2021 preferred over MDRD
- ●G6-G5: nephrology referral
- ●Monitor frequency increases with stage
Sample Clinical Scenarios
Patient Demographics
Kidney Function Markers
Clinical Information
⚠️For informational purposes only — not medical advice. Consult a healthcare professional before acting on results.
🏥 Health Facts
eGFR ≥90: normal. <60: CKD. <15: kidney failure
— KDIGO
What is Glomerular Filtration Rate (GFR)?
The Glomerular Filtration Rate (GFR) is the most important indicator of kidney function. It measures how much blood your kidneys filter per minute, expressed as mL/min/1.73m² (normalized to body surface area). GFR is used to diagnose chronic kidney disease (CKD), stage its severity, and guide treatment decisions.
KDIGO Gold Standard
GFR is the primary measure used by KDIGO guidelines for CKD classification and staging worldwide.
Normal Range:
≥90 mL/min/1.73m²
CKD-EPI 2021 Equation
The race-free CKD-EPI 2021 equation is now recommended as the standard for eGFR calculation.
Key Inputs:
Creatinine, Age, Sex
6-Stage Classification
CKD is classified into 6 stages (G1-G5) based on GFR, guiding treatment intensity and referral decisions.
Clinical Impact:
Drug dosing, dialysis timing
How GFR Calculation Works
Serum Creatinine Measurement
Blood sample analyzed for creatinine, a waste product from muscle metabolism filtered by kidneys.
Demographic Variables
Age and sex are incorporated as they affect muscle mass and creatinine production.
Equation Selection
CKD-EPI 2021 (race-free) is recommended. MDRD and Cockcroft-Gault available for comparison.
BSA Normalization
Results standardized to 1.73m² body surface area for comparison across individuals.
CKD Stage Assignment
GFR value mapped to KDIGO CKD stages (G1-G5) for clinical decision-making.
When to Calculate GFR
CKD Screening
Annual screening for diabetes, hypertension, cardiovascular disease, and family history of kidney disease
Drug Dosing
Adjust doses of renally-cleared medications based on kidney function
AKI Assessment
Baseline GFR helps distinguish acute kidney injury from chronic disease
Dialysis Planning
Track GFR decline to time dialysis initiation and transplant evaluation
Contrast Protocols
Assess risk of contrast-induced nephropathy before CT or angiography
Progression Monitoring
Track kidney function over time to assess disease progression and treatment response
GFR Estimation Formulas
CKD-EPI 2021 (Recommended)
eGFR = 142 x min(SCr/k, 1)^a x max(SCr/k, 1)^-1.200 x 0.9938^Age x [1.012 if female]Where k = 0.7 (female) or 0.9 (male); a = -0.241 (female) or -0.302 (male)
MDRD Study Equation
eGFR = 175 x SCr^-1.154 x Age^-0.203 x [0.742 if female] x [1.212 if Black]Cockcroft-Gault (Creatinine Clearance)
CrCl = [(140 - Age) x Weight (kg)] / [72 x SCr (mg/dL)] x [0.85 if female]Note: Not normalized to BSA; historically used for drug dosing
CKD Staging (KDIGO)
| Stage | GFR Range | Description |
|---|---|---|
| G1 | ≥90 | Normal or high |
| G2 | 60-89 | Mildly decreased |
| G3a | 45-59 | Mildly to moderately decreased |
| G3b | 30-44 | Moderately to severely decreased |
| G4 | 15-29 | Severely decreased |
| G5 | <15 | Kidney failure |
Frequently Asked Questions
Why was the race variable removed from CKD-EPI 2021?
Race is a social construct without clear biological basis for kidney function differences. The 2021 equation removes race to promote health equity and reduce potential for bias in clinical care.
When should I use Cockcroft-Gault vs CKD-EPI?
CKD-EPI 2021 is preferred for CKD staging. Cockcroft-Gault may still be used for drug dosing when package inserts reference creatinine clearance, though many guidelines now accept CKD-EPI.
What factors can affect eGFR accuracy?
Extreme muscle mass (athletes, amputees), acute kidney injury, pregnancy, recent meat intake, and certain medications (trimethoprim, cimetidine) can affect creatinine-based eGFR. Consider cystatin C in these cases.
What is the significance of combining creatinine and cystatin C?
Cystatin C is less affected by muscle mass than creatinine. The combined creatinine-cystatin C equation is more accurate, especially in patients with unusual muscle mass or diet.
At what GFR should nephrology referral occur?
Referral recommended for GFR <30 mL/min/1.73m², rapidly declining GFR (>5 mL/min/year), severe proteinuria (ACR >300), or uncertain etiology. Earlier referral may be appropriate for complex cases.
How often should GFR be monitored?
Annually for GFR ≥60 with no risk factors. Every 6-12 months for GFR 45-59. Every 3-6 months for GFR 30-44. Every 1-3 months for GFR <30 or rapid decline.