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  • For Educational Purposes Only: This content is intended for educational reference and should not be used for clinical decision-making.
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The clinical content and references are curated and reviewed by myself; however, AI was used to assist in organizing, paraphrasing, and formatting the information presented.
Quick Reference
  • Normal Range: ≥90 mL/min/1.73m²
  • CKD Stage 3: 30-59 mL/min/1.73m² (nephrology referral recommended)
  • Kidney Failure: <15 mL/min/1.73m² (dialysis consideration)
  • Primary Use: CKD diagnosis, staging, and monitoring progression
  • Calculation: Automatically calculated from serum creatinine, age, and sex
  • Current Standard: CKD-EPI 2021 equation (race-free)
  • Key Point: More accurate than creatinine alone; detects kidney disease earlier

What is eGFR?

The estimated Glomerular Filtration Rate (eGFR) is a calculated measure of how well the kidneys are filtering blood.

What Does eGFR Measure?

eGFR represents:

  • Filtration volume: Volume of plasma filtered by the glomeruli per minute
  • Normalized value: Standardized to body surface area (1.73m²) for comparison across individuals
  • Kidney capacity: Overall functional capacity of both kidneys combined

How is eGFR Calculated?

eGFR is calculated using validated equations that include:

  • Serum creatinine level: Primary measurement
  • Age: Accounts for decreased muscle mass with aging
  • Sex: Accounts for differences in muscle mass between males and females
  • Race (optional): Some equations include race-based adjustments

eGFR is the single best overall indicator of kidney function and is the primary metric used for diagnosing and staging chronic kidney disease (CKD).

Why Use eGFR Instead of Creatinine Alone?

  • More accurate assessment: Accounts for age, sex, and body size differences
  • Earlier detection: Can identify reduced kidney function when creatinine is still "normal"
  • Standardized staging: Enables consistent CKD classification across populations
  • Better monitoring: Small changes in eGFR reflect clinically meaningful changes in kidney function
  • Automatic reporting: Most labs automatically calculate and report eGFR with every creatinine order
Key Concept: Serum creatinine does not rise above normal until GFR has declined by approximately 50%. This means a patient can lose half of their kidney function and still have a "normal" creatinine. eGFR detects kidney impairment much earlier.
CKD Staging by eGFR

Chronic kidney disease is classified into 5 stages based on eGFR. CKD is defined as kidney damage or eGFR <60 mL/min/1.73m² for ≥3 months:

Swipe to see more
Stage eGFR (mL/min/1.73m²) Description Clinical Actions
G1 ≥90 Normal or high GFR with kidney damage* Diagnose and treat, slow progression, reduce CV risk
G2 60-89 Mild reduction in GFR with kidney damage* Estimate progression, evaluate for complications
G3a 45-59 Mild to moderate reduction Evaluate and treat complications
G3b 30-44 Moderate to severe reduction Manage complications, nephrology referral
G4 15-29 Severe reduction Prepare for renal replacement therapy
G5 <15 Kidney failure (ESRD) Renal replacement therapy (dialysis or transplant)

*Kidney damage = albuminuria, hematuria, structural abnormalities, or pathologic diagnosis

CKD Diagnosis Criteria (Must Meet Either)

  • Kidney damage ≥3 months: Albuminuria (ACR ≥30 mg/g), urine sediment abnormalities, structural abnormalities on imaging, or biopsy-proven disease
  • eGFR <60 mL/min/1.73m² for ≥3 months (with or without evidence of kidney damage)
eGFR Calculation Equations

CKD-EPI 2021 Equation (Current Standard)

Race-Free CKD-EPI Equation (Recommended as of 2021)

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

Where:
• SCr = serum creatinine (mg/dL)
• κ = 0.7 (females) or 0.9 (males)
• α = -0.241 (females) or -0.302 (males)
• min = minimum of SCr/κ or 1
• max = maximum of SCr/κ or 1

The 2021 CKD-EPI equation removed the race coefficient that was present in earlier versions. The race multiplier was eliminated because it lacked biological basis and potentially contributed to healthcare disparities.

CKD-EPI 2009 Equation (Legacy)

Original CKD-EPI with Race Coefficient (No Longer Recommended)

Same as 2021 equation, but with additional multiplication by 1.159 if Black

MDRD Equation (Legacy)

Modified Diet in Renal Disease (MDRD) - Less Accurate

eGFR = 175 × SCr-1.154 × Age-0.203 × [0.742 if female] × [1.212 if Black]

The MDRD equation is older and less accurate, especially at higher GFR values (>60 mL/min/1.73m²). Most labs have transitioned to CKD-EPI.

Which Equation to Use?

  • CKD-EPI 2021: Current gold standard, most accurate across all GFR ranges
  • MDRD: Outdated, underestimates GFR at higher values
  • Cockcroft-Gault: Estimates creatinine clearance (CrCl), NOT eGFR; used for drug dosing
Alternative GFR Markers

Cystatin C

Cystatin C is an alternative endogenous marker for GFR estimation that may be more accurate than creatinine in certain populations:

Advantages of Cystatin C

  • Less affected by muscle mass (better for elderly, amputees, malnourished)
  • More sensitive for detecting early CKD (eGFR 60-90 mL/min/1.73m²)
  • Not affected by diet or muscle metabolism
  • Can be combined with creatinine for improved accuracy (CKD-EPI Cr-Cys equation)

Limitations of Cystatin C

  • More expensive than creatinine (not routinely used)
  • Affected by thyroid disease, corticosteroid use, inflammation
  • Limited availability in some labs
  • No advantage over creatinine in most standard CKD cases

Measured GFR (Gold Standard)

For the most accurate assessment, GFR can be directly measured using exogenous filtration markers:

  • Inulin clearance: True gold standard but impractical (requires IV infusion, timed urine collection)
  • Iohexol clearance: Practical alternative for research or complex cases
  • 51Cr-EDTA or 125I-iothalamate: Nuclear medicine methods

Measured GFR is rarely needed in clinical practice and reserved for kidney donation evaluation, clinical trials, or when eGFR accuracy is questionable.

Albuminuria Categories

CKD is staged using both eGFR (G stage) and albuminuria (A stage), e.g., "CKD G3b A2"

Swipe to see more
Category ACR (mg/g) Description
A1 <30 Normal to mildly increased
A2 30-300 Moderately increased (microalbuminuria)
A3 >300 Severely increased (macroalbuminuria)
Clinical Interpretation

When to Be Concerned About eGFR

Swipe to see more
eGFR Range Clinical Significance Action Required
≥90 Normal (if no other evidence of kidney damage) Routine monitoring if risk factors present
60-89 Mild reduction (only CKD if kidney damage present) Screen for albuminuria, evaluate for progression
45-59 CKD Stage 3a (moderate reduction) Evaluate complications, optimize BP/diabetes control
30-44 CKD Stage 3b (moderate-severe reduction) Nephrology referral, manage complications
15-29 CKD Stage 4 (severe reduction) Prepare for dialysis, transplant evaluation
<15 CKD Stage 5 (kidney failure) Dialysis or transplant required for survival
Limitations of eGFR

Situations Where eGFR May Be Inaccurate

  • Acute kidney injury: eGFR assumes steady-state creatinine; rapidly changing creatinine makes eGFR unreliable
  • Extremes of body size: Very obese, very thin, amputees, or very muscular individuals
  • Extremes of age: Children (<18 years require pediatric equations) and very elderly
  • Dietary extremes: Vegan/vegetarian diets (lower creatinine production), high protein diets
  • Severe malnutrition or muscle wasting: Cachexia, cirrhosis, neuromuscular disease
  • Paraplegia/quadriplegia: Reduced muscle mass
  • Pregnancy: Increased GFR (eGFR underestimates true GFR)
  • Edematous states: Volume overload may dilute creatinine

Medications That Affect eGFR Accuracy

  • Trimethoprim, cimetidine: Block tubular secretion, increase creatinine without affecting true GFR
  • Creatine supplements: Increase creatinine production
  • Cephalosporins (high dose): Interfere with creatinine assay

In these situations, consider:

  • 24-hour urine creatinine clearance
  • Cystatin C-based eGFR
  • Measured GFR using exogenous markers (inulin, iohexol)
Clinical Pearls
eGFR is automatically reported: Most labs calculate eGFR from every serum creatinine ordered. You don't need to order it separately.
eGFR >60 alone is NOT diagnostic of CKD: Stages G1 and G2 require evidence of kidney damage (albuminuria, hematuria, imaging findings). Don't label patients as CKD without additional findings!
3-month rule: CKD requires abnormalities persisting ≥3 months. A single low eGFR does not diagnose CKD - recheck before diagnosing.
eGFR in acute settings: Do NOT rely on eGFR during AKI or rapidly changing kidney function. Use absolute creatinine and KDIGO AKI criteria instead.
Age-related decline: GFR physiologically declines ~1 mL/min/1.73m² per year after age 40. Elderly patients commonly have eGFR 60-89 without true kidney disease.
"Rule of thumb" for medication dosing: Many drugs require dose adjustment when eGFR <60 mL/min/1.73m². Always check renal dosing guidelines.
eGFR vs CrCl for drug dosing: Pharmacokinetic studies often used Cockcroft-Gault (CrCl), not eGFR. Package inserts may specify which to use - read carefully!
Race and eGFR: The 2021 race-free equation may slightly underestimate GFR in Black patients compared to the old equation. Clinical significance is debated but removing race was deemed more equitable.
Hyperfiltration (eGFR >120-130): May be seen in early diabetes, pregnancy, or high protein intake. Can actually precede diabetic nephropathy - a warning sign!
Small changes matter: A decline of 5 mL/min/1.73m² per year indicates progressive CKD and warrants investigation.
Always check trends: Compare current eGFR to previous values. A stable eGFR of 55 is very different from a rapidly declining eGFR. Trend is everything!
References
  1. Kratz, A., Ferraro, M., Sluss, P. M., & Lewandrowski, K. B. (2004). Laboratory reference values. New England Journal of Medicine, 351, 1548-1564.
  2. Lee, M. (Ed.). (2009). Basic skills in interpreting laboratory data. Ashp.
  3. Farinde, A. (2021). Lab values, normal adult: Laboratory reference ranges in healthy adults. Medscape.
  4. Nickson, C. (n.d.). Critical Care Compendium. Life in the Fast Lane • LITFL.
  5. Farkas, Josh MD. (2015). Table of Contents - EMCrit Project. EMCrit Project.
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