Is a Glomerular Filtration Rate (GFR) of 137 considered normal?

Is a GFR of 137 Normal?

Yes, a GFR of 137 mL/min/1.73 m² is normal and may even be considered high-normal, as it falls within the G1 category (≥90 mL/min/1.73 m²) according to the Kidney Disease: Improving Global Outcomes (KDIGO) guidelines. 1

Understanding GFR Values

GFR values are categorized as follows:

• G1 (≥90 mL/min/1.73 m²): Normal or high kidney function
• G2 (60-89 mL/min/1.73 m²): Mildly decreased kidney function
• G3a (45-59 mL/min/1.73 m²): Mildly to moderately decreased
• G3b (30-44 mL/min/1.73 m²): Moderately to severely decreased
• G4 (15-29 mL/min/1.73 m²): Severely decreased
• G5 (<15 mL/min/1.73 m²): Kidney failure

Normal GFR Reference Ranges

The normal reference range for GFR varies by age, sex, and body size:

• Young adult males: 120-130 mL/min/1.73 m² 1
• Young adult females: 90-120 mL/min/1.73 m² 1

A GFR of 137 mL/min/1.73 m² is therefore within the normal range but at the higher end, which could represent:

1. Normal variation in a healthy individual
2. Possible renal hyperfiltration in certain contexts

Interpreting High-Normal GFR Values

While a GFR of 137 mL/min/1.73 m² is not concerning in most cases, it's important to understand that:

• GFR naturally declines with age at approximately 0.75-0.8 mL/min/year after age 40 1
• Very high GFR values may sometimes represent renal hyperfiltration, which has been associated with early phases of kidney disease in conditions such as obesity and diabetes 2

Important Considerations

1. Measurement Accuracy: All GFR measurements and estimations have inherent variability:

   • Biological variability exists in both measured GFR (mGFR) and estimated GFR (eGFR) 3
   • The CKD-EPI equation is more accurate for GFR >60 mL/min/1.73 m² 1

2. Context Matters: A single GFR value should be interpreted in the clinical context:

   • Age of the patient
   • Presence of other risk factors for kidney disease
   • Other laboratory values (e.g., urinary albumin-to-creatinine ratio)

3. Follow-up: If there are concerns about hyperfiltration or other kidney issues:

   • Repeat testing may be warranted to confirm findings
   • Assessment of albuminuria is recommended to evaluate for early kidney damage 4

When to Be Concerned

While a GFR of 137 mL/min/1.73 m² is not typically concerning, monitoring would be appropriate if:

• The patient has diabetes (where hyperfiltration may precede diabetic kidney disease)
• There is evidence of albuminuria (UACR ≥30 mg/g creatinine)
• The patient has other risk factors for kidney disease
• The elevated GFR persists on repeated measurements

In conclusion, a GFR of 137 mL/min/1.73 m² falls within the normal range (G1 category) and generally represents good kidney function, though context and other clinical parameters should always be considered in the overall assessment.