Stages of Chronic Kidney Disease (CKD)
Chronic Kidney Disease is classified into five stages based on glomerular filtration rate (GFR) and three albuminuria categories, with comprehensive risk assessment requiring evaluation of both parameters to guide management decisions. 1
Definition of CKD
CKD is defined as either:
- Kidney damage persisting for ≥3 months, with or without decreased GFR, OR
- GFR <60 mL/min/1.73 m² persisting for ≥3 months, with or without evidence of kidney damage 1
GFR Stages (G1-G5)
| Stage | GFR (mL/min/1.73 m²) | Description |
|---|---|---|
| G1 | ≥90 | Normal or elevated GFR with evidence of kidney damage |
| G2 | 60-89 | Mildly decreased GFR with evidence of kidney damage |
| G3a | 45-59 | Mildly to moderately decreased GFR |
| G3b | 30-44 | Moderately to severely decreased GFR |
| G4 | 15-29 | Severely decreased GFR |
| G5 | <15 | Kidney failure |
Albuminuria Categories (A1-A3)
| Category | Albumin-to-Creatinine Ratio (mg/g) | Description |
|---|---|---|
| A1 | <30 | Normal to mildly increased |
| A2 | 30-300 | Moderately increased |
| A3 | >300 | Severely increased |
Comprehensive CKD Classification
The Kidney Disease: Improving Global Outcomes (KDIGO) recommends a comprehensive CKD staging system that incorporates both GFR stages and albuminuria categories 2. This combined approach provides better risk stratification for:
- CKD progression
- Cardiovascular disease risk
- Mortality risk
Clinical Focus by Stage
- Stage G1-G2 with A1: Monitor annually, focus on risk reduction
- Stage G1-G2 with A2-A3: Treat and monitor more frequently (2-4 times/year)
- Stage G3a-G3b: Evaluate for complications, monitor progression, treat comorbidities
- Stage G4: Manage complications, prepare for kidney replacement therapy
- Stage G5: Consider kidney replacement therapy if uremic symptoms present
Referral to Nephrology
Prompt referral to nephrology is recommended for:
- GFR <30 mL/min/1.73 m² (Stage G4-G5)
- Albuminuria ≥300 mg/g (A3 category)
- Rapid decline in GFR
- Persistent hematuria
- Uncontrolled hypertension
- Suspected genetic kidney disease 1
Screening and Monitoring
- For patients with type 1 diabetes: Begin screening 5 years after diagnosis
- For patients with type 2 diabetes: Begin screening at time of diagnosis
- For patients with hypertension or cardiovascular disease: Regular screening recommended 1
Common Pitfalls and Caveats
Misclassification risk: Single measurements of GFR or albuminuria can lead to misclassification. Confirmation with repeat testing over 3 months is required for diagnosis.
Age considerations: Decreased GFR in elderly patients may represent normal aging rather than disease, but still predicts adverse outcomes and requires appropriate management.
Measurement methods: Urinary albumin-to-creatinine ratio (UACR) from a random spot urine sample is preferred over timed collections, which add little to prediction accuracy but increase burden 2.
Interpretation challenges: At any GFR level, the degree of albuminuria is associated with risk of cardiovascular disease, CKD progression, and mortality, highlighting the importance of assessing both parameters 2.
Retinopathy correlation: In type 1 diabetes, kidney disease rarely develops without retinopathy. In type 2 diabetes, retinopathy is only moderately sensitive for CKD diagnosis 2.
The comprehensive staging system using both GFR and albuminuria provides a more accurate risk assessment and guides treatment decisions more effectively than using GFR alone.