Normal Range for Glomerular Filtration Rate (GFR)
The normal GFR range is ≥90 mL/min/1.73 m² for adults, with young adult males typically having values of 120-130 mL/min/1.73 m² and young adult females having values of 90-120 mL/min/1.73 m². 1
Age-Related GFR Variations
GFR naturally changes with age, following this pattern:
- Young adults (under 40 years): Approximately 107-130 mL/min/1.73 m² 1, 2
- Adults over 40: GFR declines at a rate of approximately 0.75-0.8 mL/min/year 1
- Elderly (over 70): Values below 60 mL/min/1.73 m² may be physiologically normal 3
GFR Classification System
According to KDIGO guidelines, GFR is categorized as follows 4:
| GFR Category | Description | 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 |
Clinical Interpretation of GFR Values
- GFR ≥90 mL/min/1.73 m²: Normal kidney function 4
- GFR 60-89 mL/min/1.73 m²: Mildly decreased kidney function, may be normal for elderly 4
- GFR <60 mL/min/1.73 m²: Represents loss of half or more of normal kidney function and is classified as chronic kidney disease (CKD) 1
Important Considerations When Interpreting GFR
- Serum creatinine alone is an unreliable indicator of kidney function, as GFR must decline to approximately half the normal level before serum creatinine rises above the upper limit of normal 1
- GFR estimation equations (eGFR) have different accuracy ranges:
Common Pitfalls in GFR Interpretation
- Age effect: Not accounting for the natural decline in GFR with age can lead to overdiagnosis of CKD in elderly patients 3
- Estimation errors: eGFR formulas may significantly underestimate true GFR in people with normal kidney function, particularly those with GFR ≥90 mL/min/1.73 m² 5
- Method variability: Different methods of measuring GFR (isotopic, clearance, estimation equations) can yield different results 6
- Body size impact: GFR is standardized to body surface area of 1.73 m², which may not be appropriate for all individuals
Remember that while 60 mL/min/1.73 m² is often used as a fixed cutoff for defining CKD, this approach may not adequately account for age-related changes in kidney function, particularly in adults over 70 years 3.