Recommended GFR for Elderly in Their 90s
For individuals in their 90s, a GFR between 30-59 mL/min/1.73 m² (Stage 3 CKD) can be considered normal and physiologically appropriate for their age. 1
Age-Related Changes in Kidney Function
Kidney function naturally declines with age due to several physiological changes:
- Decreased number of functional glomeruli due to nephrosclerosis 2
- Smaller cortical volume and increased prevalence of kidney cysts 2
- Loss of approximately 16.6 mL/min/1.73 m² per decade after age 75 3
- Accelerated decline between ages 80-85 3
Normal GFR Ranges by Age
The Kidney Disease: Improving Global Outcomes (KDIGO) classification system defines CKD stages as:
| Stage | Description | GFR (mL/min/1.73 m²) |
|---|---|---|
| 1 | Normal or increased GFR | ≥90 |
| 2 | Mild decrease in GFR | 60-89 |
| 3a | Mild to moderate decrease | 45-59 |
| 3b | Moderate to severe decrease | 30-44 |
| 4 | Severe decrease | 15-29 |
| 5 | Kidney failure | <15 or dialysis |
While this classification applies to all adults, it's important to recognize that:
- In adults over 70 years, GFR values below 60 mL/min/1.73 m² may be considered normal 4
- By age 85, most women have eGFR ranging from 30-89 mL/min/1.73 m² (Stage 2-3) 3
- For individuals ≥65 years, the lowest mortality risk is associated with a GFR of 45-104 mL/min/1.73 m² 2
Measurement Considerations for the Elderly
When assessing GFR in nonagenarians:
- Serum creatinine alone is unreliable and significantly underestimates renal insufficiency in the elderly 1
- Creatinine-based formulas may be less accurate due to decreased muscle mass in the elderly 1
- The MDRD and CKD-EPI equations tend to overestimate GFR in the elderly 5
- Consider using the combination of creatinine and cystatin C (eGFRcr-cys) for more accurate estimation 6
Clinical Implications
For elderly patients in their 90s:
- A moderate decrease in GFR (30-59 mL/min/1.73 m²) should not automatically be classified as disease 4
- GFR <45 mL/min/1.73 m² (Stage 3B) is associated with significantly increased mortality risk and should prompt closer monitoring 3
- Medication dosing should be adjusted according to estimated GFR to avoid toxicity 1, 6
- Monitor for complications of reduced GFR including anemia, mineral bone disease, and metabolic acidosis 6
Common Pitfalls to Avoid
- Misdiagnosing CKD in the elderly based on fixed GFR cutoffs without considering age-related changes 2
- Relying solely on serum creatinine, which can appear normal despite significantly reduced GFR 1
- Using inappropriate estimation equations that don't account for age-related changes in body composition 5
- Failing to recognize that elderly patients have reduced kidney functional reserve when they develop acute kidney injury 2
In conclusion, while the standard CKD classification system defines Stage 3 (GFR 30-59 mL/min/1.73 m²) as moderate kidney disease, this range can represent normal kidney function for individuals in their 90s, reflecting the natural aging process rather than pathology.