Stages of Chronic Kidney Disease
Chronic kidney disease (CKD) is classified into five distinct stages based primarily on glomerular filtration rate (GFR), with additional consideration for markers of kidney damage such as albuminuria. 1
Definition of CKD
CKD is defined as either:
- GFR less than 60 mL/min/1.73 m² persisting for at least 3 months, OR
- Evidence of kidney damage persisting for at least 3 months, regardless of GFR 2
Markers of kidney damage include:
- Albuminuria (albumin-to-creatinine ratio ≥30 mg/g)
- Abnormalities in urine sediment
- Electrolyte abnormalities due to tubular disorders
- Abnormalities detected by histology
- Structural abnormalities detected by imaging
- History of kidney transplantation 1
The Five Stages of CKD
| Stage | GFR (mL/min/1.73 m²) | Description | Clinical Focus |
|---|---|---|---|
| 1 | ≥90 | Normal or elevated GFR with evidence of kidney damage | Diagnosis, risk reduction, treating comorbidities |
| 2 | 60-89 | Mildly decreased GFR with evidence of kidney damage | Slowing progression, CVD risk reduction |
| 3 | 30-59 | Moderately decreased GFR | Evaluating complications, estimating progression |
| 4 | 15-29 | Severely decreased GFR | Managing complications, preparing for replacement therapy |
| 5 | <15 or dialysis | Kidney failure | Replacement therapy if uremia present |
Important Refinements to Staging
Modern guidelines further subdivide Stage 3 into:
- Stage 3a: GFR 45-59 mL/min/1.73 m² (Mildly to moderately decreased)
- Stage 3b: GFR 30-44 mL/min/1.73 m² (Moderately to severely decreased) 1
This subdivision is clinically important as Stage 3b carries a significantly higher risk of progression to more advanced stages and requires closer monitoring 1.
Albuminuria Categories
Current guidelines recommend incorporating albuminuria assessment into CKD staging for better risk stratification:
| Category | Albumin-to-Creatinine Ratio (mg/g) | Description |
|---|---|---|
| A1 | <30 | Normal to mildly increased |
| A2 | 30-300 | Moderately increased |
| A3 | >300 | Severely increased |
Clinical Implications of CKD Stages
Each stage requires specific clinical focus and interventions:
Stage 1 (GFR ≥90 mL/min/1.73 m²)
Stage 2 (GFR 60-89 mL/min/1.73 m²)
- Continue Stage 1 interventions
- Implement strategies to slow progression
- Cardiovascular disease risk reduction 2, 1
Stage 3 (GFR 30-59 mL/min/1.73 m²)
- Continue previous interventions
- Begin evaluation for complications
- Estimate progression rate
- More frequent monitoring of kidney function 2, 1
Stage 4 (GFR 15-29 mL/min/1.73 m²)
- Manage complications (anemia, bone disorders, etc.)
- Prepare for renal replacement therapy
- Consider nephrology referral if not already done
- Review medications for appropriate dosing 2, 1
Stage 5 (GFR <15 mL/min/1.73 m² or dialysis)
- Implement renal replacement therapy when indicated
- Manage uremic symptoms
- Consider transplant evaluation 2, 1
Epidemiology
The prevalence of CKD in the United States is significant, with approximately 11% of the adult population (20 million persons) having some form of CKD 2. The prevalence of early stages (1-4) is more than 100 times greater than kidney failure (stage 5) 2.
Clinical Pitfalls to Avoid
Relying solely on serum creatinine: Serum creatinine alone can lead to gross overestimation of kidney function, as some patients maintain seemingly normal creatinine levels despite declining GFR 2.
Ignoring albuminuria: Even with normal GFR, persistent albuminuria indicates kidney damage and increased risk for CKD progression 1.
Medication errors: Failure to adjust medication doses according to CKD stage can lead to adverse effects, particularly in Stage 3b and beyond 1.
Dismissing mild GFR reduction in elderly: While GFR naturally declines with age, decreased GFR in the elderly remains an independent predictor of adverse outcomes and requires appropriate management 2.
By understanding and appropriately applying the CKD staging system, clinicians can better identify patients at risk, implement appropriate interventions, and potentially slow disease progression while reducing complications.