Definition of Severe Renal Impairment
Severe renal impairment is defined as a glomerular filtration rate (GFR) of 15-29 mL/min/1.73 m².1
Classification of Renal Function Based on GFR
Renal function is categorized into stages based on estimated glomerular filtration rate (eGFR) values:
| CKD Stage | Description | eGFR (mL/min/1.73 m²) |
|---|---|---|
| 1 | Normal or increased GFR with kidney damage | ≥90 |
| 2 | Slightly decreased GFR with kidney damage | 60-89 |
| 3a | Mild to moderate GFR decrease | 45-59 |
| 3b | Moderate to severe GFR decrease | 30-44 |
| 4 | Severe GFR decrease | 15-29 |
| 5 | Kidney failure | <15 or dialysis |
Clinical Implications of Severe Renal Impairment
Severe renal impairment (GFR 15-29 mL/min/1.73 m²) has significant clinical implications:
Renal Replacement Therapy: Patients with eGFR <30 mL/min/1.73 m² should be considered for dialysis therapy or transplantation 1
Medication Adjustments: Many medications require dose adjustments or are contraindicated at this level of renal function
- Example: Metformin is contraindicated when eGFR falls below 30 mL/min/1.73 m² due to increased risk of lactic acidosis 2
Cardiovascular Risk: Severe renal impairment significantly increases cardiovascular morbidity and mortality 3
Mortality Risk: The adjusted risk of in-hospital mortality is significantly higher in patients with severe renal insufficiency (GFR <30 mL/min/1.73 m²) compared to those with normal renal function 4
Monitoring and Management
For patients with severe renal impairment:
- Monitor serum creatinine, eGFR, electrolytes, and urine albumin-to-creatinine ratio regularly 3
- Assess GFR and albuminuria more frequently than the standard annual recommendation 3
- Maintain protein intake at approximately 0.8 g/kg/day 1, 3
- Consider referral to nephrology for specialized care and preparation for potential renal replacement therapy
- Implement strict blood pressure control with target <125/75 mmHg 3
Common Pitfalls to Avoid
Relying solely on serum creatinine: Creatinine levels can appear near normal despite significant renal impairment, especially in elderly or malnourished patients with reduced muscle mass
Delayed recognition: Failing to recognize severe renal impairment may lead to inappropriate medication dosing and delayed preparation for renal replacement therapy
Inadequate monitoring: Patients with GFR 15-29 mL/min/1.73 m² require more frequent monitoring than those with milder renal impairment
Nephrotoxic medications: Continuing nephrotoxic medications in patients with severe renal impairment can accelerate progression to end-stage renal disease
Remember that kidney injury is not defined solely by GFR but also includes evidence of albuminuria (UACR ≥30 mg/g) or abnormalities in pathological, urine, blood, or imaging examinations 1.