Stages of Chronic Kidney Disease (CKD)
Chronic Kidney Disease is classified into five stages based on glomerular filtration rate (GFR) and evidence of kidney damage, with each stage requiring specific monitoring and interventions as kidney function progressively declines.
CKD Classification System
The Kidney Disease: Improving Global Outcomes (KDIGO) guidelines define CKD stages as follows:
Stage 1: GFR ≥90 mL/min/1.73 m²
- Definition: Normal kidney function but with evidence of kidney damage
- Required evidence: Must have markers of kidney damage (e.g., albuminuria, abnormal urinary sediment, structural abnormalities on imaging, or pathological abnormalities on biopsy) 1
- Clinical focus: Diagnosis of underlying cause, CKD risk reduction, treatment of comorbid conditions 1
Stage 2: GFR 60-89 mL/min/1.73 m²
- Definition: Mildly decreased kidney function with evidence of kidney damage
- Required evidence: Same markers of kidney damage as Stage 1
- Clinical focus: Slowing progression, cardiovascular disease risk reduction 1
Stage 3: GFR 30-59 mL/min/1.73 m²
- Definition: Moderately decreased kidney function
- Subdivisions:
- Note: At this stage, CKD can be diagnosed by GFR alone, without other evidence of kidney damage 1
- Clinical focus: Evaluation and treatment of complications (anemia, bone disorders, metabolic acidosis) 1
Stage 4: GFR 15-29 mL/min/1.73 m²
- Definition: Severely decreased kidney function
- Clinical focus: Preparation for renal replacement therapy, management of uremic complications 1
Stage 5: GFR <15 mL/min/1.73 m² or dialysis
- Definition: Kidney failure (also called end-stage renal disease when treated with dialysis or transplantation) 1
- Clinical focus: Renal replacement therapy (if uremia present), management of complications 1
Clinical Implications of CKD Stages
Prevalence and Risk
- Approximately 10-13% of the global population has some stage of CKD 2, 3
- Early stages (1-4) are over 100 times more common than kidney failure (stage 5) 1
- Risk of complications increases progressively with declining GFR 1
Complications by Stage
- Stages 1-2: Generally few symptoms; focus on prevention
- Stage 3: Increasing prevalence of hypertension, early metabolic abnormalities
- Stage 4: Higher prevalence of anemia, bone disorders, metabolic acidosis, hypertension
- Stage 5: Multiple complications including uremia, severe anemia, renal osteodystrophy, electrolyte disturbances, and cardiovascular complications 1
Clinical Action Plan by Stage
- Stages 1-2: Diagnosis of underlying cause, risk factor modification
- Stage 3: Regular monitoring of GFR and complications, treatment of comorbidities
- Stage 4: Preparation for renal replacement therapy, management of complications
- Stage 5: Implementation of renal replacement therapy (dialysis or transplantation) when clinically indicated 1
Important Clinical Considerations
- CKD diagnosis requires persistence of abnormalities for at least 3 months 1
- Albuminuria is an important marker of kidney damage and should be assessed in all patients 1
- Diabetes and hypertension are the leading causes of CKD worldwide 1
- The risk of cardiovascular disease increases substantially as CKD progresses 1, 4
Common Pitfalls in CKD Staging
- Relying on serum creatinine alone: GFR estimation formulas are more accurate than serum creatinine alone
- Missing early CKD: Stages 1-2 require evidence of kidney damage despite normal or near-normal GFR
- Failing to recognize age-related GFR decline: While GFR naturally declines with age, this should not be dismissed as normal aging when other evidence of kidney damage is present 1
- Overlooking albuminuria: Even with normal GFR, persistent albuminuria indicates kidney damage and increased risk 1
By understanding and appropriately applying the CKD staging system, clinicians can implement stage-specific interventions to slow disease progression, manage complications, and improve patient outcomes.