The estimated Glomerular Filtration Rate (eGFR) is one of the most important tests for assessing kidney function. Understanding your eGFR results can help you and your healthcare provider monitor kidney health and detect chronic kidney disease early.

What is eGFR?

The estimated Glomerular Filtration Rate (eGFR) is a measure of how well your kidneys are filtering waste and excess water from your blood. It's calculated using a formula that considers your serum creatinine level, age, sex, and race.

Key Points About eGFR

Units: Measured in mL/min/1.73m² (milliliters per minute per 1.73 square meters of body surface area)

Normal Range: 90 mL/min/1.73m² or higher in healthy adults

Calculation: Based on serum creatinine, age, sex, and race

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Understanding eGFR Values

eGFR values are used to classify kidney function into different stages:

Stage eGFR (mL/min/1.73m²) Description Action Needed
Stage 1 ≥90 Normal or high kidney function Monitor if kidney damage present
Stage 2 60-89 Mildly decreased kidney function Monitor and treat risk factors
Stage 3a 45-59 Mild to moderate decrease Evaluate and treat complications
Stage 3b 30-44 Moderate to severe decrease Prepare for kidney replacement therapy
Stage 4 15-29 Severe decrease in kidney function Prepare for dialysis or transplant
Stage 5 <15 Kidney failure Dialysis or transplant needed

How is eGFR Calculated?

Several equations are used to calculate eGFR, with the most common being:

CKD-EPI Equation (2021)

The most current and widely recommended equation that removes race as a factor:

  • For females: eGFR = 142 × min(Scr/0.7, 1)^(-0.241) × max(Scr/0.7, 1)^(-1.200) × 0.9938^age
  • For males: eGFR = 142 × min(Scr/0.9, 1)^(-0.302) × max(Scr/0.9, 1)^(-1.200) × 0.9938^age

MDRD Equation

An older equation still sometimes used:

  • eGFR = 175 × (Scr)^(-1.154) × (Age)^(-0.203) × (0.742 if female)

Factors Affecting eGFR Accuracy

Several factors can influence the accuracy of eGFR calculations:

Muscle Mass

Very high or low muscle mass can affect creatinine levels and eGFR accuracy.

Diet

High protein intake or creatine supplements can temporarily increase creatinine.

Medications

Some drugs can affect creatinine levels without changing actual kidney function.

Acute Illness

Dehydration or acute kidney injury can temporarily alter eGFR.

When to Test eGFR

Regular eGFR testing is recommended for:

  • People with diabetes: Annual testing recommended
  • People with high blood pressure: Regular monitoring
  • Family history of kidney disease: Periodic screening
  • Age over 60: Consider regular testing
  • Cardiovascular disease: Monitor kidney function
  • Taking nephrotoxic medications: Regular monitoring

Interpreting Your Results

Understanding what your eGFR results mean:

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Normal eGFR (≥90 mL/min/1.73m²)

  • Indicates good kidney function
  • Continue healthy lifestyle habits
  • Monitor if other signs of kidney damage are present

Mildly Decreased eGFR (60-89 mL/min/1.73m²)

  • May be normal for older adults
  • Monitor for progression
  • Address risk factors like diabetes and hypertension

Moderately Decreased eGFR (30-59 mL/min/1.73m²)

  • Indicates chronic kidney disease
  • Requires medical evaluation and management
  • May need specialist referral

Severely Decreased eGFR (<30 mL/min/1.73m²)

  • Advanced chronic kidney disease
  • Requires nephrology consultation
  • Preparation for renal replacement therapy may be needed

Protecting Your Kidney Function

Steps to maintain healthy kidney function:

Control Blood Pressure

Keep blood pressure below 130/80 mmHg, or as recommended by your doctor.

Manage Diabetes

Maintain good blood sugar control with HbA1c <7% (or as advised).

Healthy Diet

Follow a balanced diet low in sodium and processed foods.

Stay Hydrated

Drink adequate water unless fluid restriction is recommended.

Medications and Kidney Function

Some medications require dose adjustment based on eGFR:

Medication Class Considerations Monitoring
ACE Inhibitors/ARBs May cause temporary eGFR decrease Check eGFR 1-2 weeks after starting
Metformin Avoid if eGFR <30 Regular kidney function monitoring
NSAIDs Can worsen kidney function Use with caution, monitor closely
Contrast Agents Risk of contrast nephropathy Pre and post-procedure monitoring

Monitoring Progression

Regular monitoring helps track kidney function over time:

Testing Frequency

  • Stage 1-2: Annually or as recommended
  • Stage 3a: Every 6-12 months
  • Stage 3b-4: Every 3-6 months
  • Stage 5: Monthly or as needed

Additional Tests

  • Urine albumin: Detects early kidney damage
  • Blood pressure: Monitor cardiovascular health
  • Electrolytes: Check for imbalances
  • Hemoglobin: Screen for anemia

When to See a Specialist

Consider nephrology referral when:

  • eGFR <30 mL/min/1.73m² (Stage 4-5 CKD)
  • Rapid decline in eGFR (>5 mL/min/1.73m² per year)
  • Significant proteinuria (albumin-to-creatinine ratio >300 mg/g)
  • Difficult-to-control blood pressure
  • Recurrent kidney stones
  • Hereditary kidney disease

Conclusion

eGFR is a valuable tool for monitoring kidney health and detecting chronic kidney disease early. Regular testing, combined with appropriate lifestyle modifications and medical management, can help preserve kidney function and prevent complications. Always discuss your results with your healthcare provider to understand what they mean for your individual situation.

Calculate Your eGFR

Use our eGFR calculator to estimate your kidney function based on your latest lab results.

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