Normal GFR Ranges for Adults
Normal GFR in adults ranges from 90-120 mL/min/1.73 m² for those under 40 years of age, with values progressively declining after age 40, and values between 60-89 mL/min/1.73 m² considered mildly decreased. 1
GFR Categories According to KDIGO Guidelines
The Kidney Disease: Improving Global Outcomes (KDIGO) classification system defines GFR categories as follows:
| GFR Category | Description | GFR Range (mL/min/1.73 m²) |
|---|---|---|
| G1 | Normal or high | ≥90 |
| G2 | Mildly decreased | 60-89 |
| G3a | Mildly to moderately decreased | 45-59 |
| G3b | Moderately to severely decreased | 30-44 |
| G4 | Severely decreased | 15-29 |
| G5 | Kidney failure | <15 or on dialysis |
Age-Related Considerations in GFR
- Under 40 years: GFR typically remains stable at approximately 107 mL/min/1.73 m² 3
- Over 40 years: GFR begins to decline physiologically by approximately:
- 0.7-0.9 mL/min/1.73 m² per year in healthy individuals
- 1.0-1.2 mL/min/1.73 m² per year in those with health conditions 4
It's important to note that while GFR declines with age, this decline is more pronounced in individuals with health conditions. However, even healthy aging is associated with lower GFR in older adults 4.
Clinical Implications of GFR Categories
- GFR ≥90 mL/min/1.73 m²: Generally considered normal kidney function, though CKD diagnosis requires additional markers of kidney damage (e.g., albuminuria) 1, 2
- GFR 60-89 mL/min/1.73 m²: Mildly decreased GFR, but may be appropriate for age in older adults; requires evidence of kidney damage for CKD diagnosis 2
- GFR <60 mL/min/1.73 m²: Considered abnormal in most adults and meets criteria for CKD regardless of other markers, though may be physiologically appropriate in adults over 70 years 5
Diagnostic Considerations
When assessing GFR, several factors should be considered:
- The CKD-EPI equation is recommended for reporting eGFR in adults as it has less bias than the MDRD equation, especially at GFR ≥60 mL/min/1.73 m² 1
- For individuals with eGFRcreat 45-59 mL/min/1.73 m² without other markers of kidney damage, measuring cystatin C for confirmation may be useful 1
- GFR should be interpreted alongside albuminuria for comprehensive kidney function assessment 1
Risk Stratification
The combination of GFR and albuminuria provides better risk stratification for CKD progression and cardiovascular outcomes:
- Low risk: GFR ≥60 mL/min/1.73 m² with normal/mildly increased albuminuria (<30 mg/g)
- Moderate risk: GFR ≥60 mL/min/1.73 m² with moderately increased albuminuria (30-299 mg/g) OR GFR 45-59 mL/min/1.73 m² with normal/mildly increased albuminuria
- High risk: Various combinations of decreased GFR and increased albuminuria
- Very high risk: Severely decreased GFR (<30 mL/min/1.73 m²) with any degree of albuminuria 1
Monitoring Recommendations
Frequency of GFR monitoring should be based on the risk category:
- Low risk: Annual monitoring
- Moderate risk: 1-2 times per year
- High risk: 2-3 times per year
- Very high risk: 3-4 times per year 1
In summary, while normal GFR is generally considered ≥90 mL/min/1.73 m², interpretation must consider age, presence of albuminuria, and other clinical factors. The physiological decline in GFR with aging means that lower values may be normal in older adults, but values <60 mL/min/1.73 m² generally warrant clinical attention regardless of age.