Staging of Chronic Kidney Disease (CKD) Based on GFR
Chronic Kidney Disease is classified into five stages based primarily on glomerular filtration rate (GFR), with additional consideration of albuminuria for comprehensive risk assessment. 1
GFR-Based CKD Staging
| Stage | Description | GFR (mL/min/1.73 m²) |
|---|---|---|
| G1 | Normal or high kidney function with evidence of kidney damage | ≥90 |
| G2 | Mildly decreased kidney function with evidence of kidney damage | 60-89 |
| G3a | Mildly to moderately decreased kidney function | 45-59 |
| G3b | Moderately to severely decreased kidney function | 30-44 |
| G4 | Severely decreased kidney function | 15-29 |
| G5 | Kidney failure | <15 |
For stages G1 and G2, evidence of kidney damage (such as albuminuria, abnormal imaging, or other markers) must be present for at least 3 months to diagnose CKD, as GFR alone may be normal or only mildly reduced 1.
Albuminuria Categories in CKD Classification
Albuminuria is an important component of CKD classification and risk stratification:
| Category | Description | Albumin-to-Creatinine Ratio (ACR) |
|---|---|---|
| A1 | Normal to mildly increased | <30 mg/g |
| A2 | Moderately increased | 30-299 mg/g |
| A3 | Severely increased | ≥300 mg/g |
Comprehensive CKD Assessment
The KDIGO guidelines recommend using both GFR and albuminuria to assess prognosis and guide clinical decision-making 1. This combined approach provides better risk stratification for:
- CKD progression
- Cardiovascular events
- Mortality
Clinical Implications of CKD Stages
Each stage carries specific clinical implications:
- G1-G2 with albuminuria: Early kidney damage requiring monitoring and risk factor management
- G3a-G3b: Increased risk of complications including hypertension, anemia, and bone disorders
- G4: High risk of progression to kidney failure; referral to nephrology recommended
- G5: Kidney failure requiring preparation for kidney replacement therapy
Important Considerations in CKD Staging
GFR Estimation: The CKD-EPI equation is currently the most accurate formula for estimating GFR, especially at higher GFR values 2, 3.
Age Considerations: While GFR naturally declines with age, decreased GFR in the elderly is still an independent predictor of adverse outcomes and requires the same staging approach 1.
Persistence Requirement: CKD diagnosis requires abnormalities to be present for at least 3 months to distinguish from acute kidney injury 4.
Kidney Failure vs. ESRD: Kidney failure (GFR <15 mL/min/1.73 m²) is not synonymous with End-Stage Renal Disease (ESRD), which is an administrative term indicating treatment with dialysis or transplantation 1.
Risk Assessment: The combination of GFR category and albuminuria category provides a more comprehensive assessment of risk than either parameter alone 1.
Monitoring and Referral Guidelines
Based on CKD stage, the following monitoring frequencies are recommended 1:
- G1-G2 with normal albuminuria: Annual monitoring
- G3a with normal albuminuria: Annual monitoring
- G3a with increased albuminuria: Twice yearly monitoring
- G3b: Twice yearly monitoring
- G4: Three to four times yearly monitoring
- G5: Four times yearly monitoring
Nephrology referral is recommended for:
- GFR <30 mL/min/1.73 m² (G4-G5)
- Persistent significant albuminuria (A3)
- Rapid GFR decline (>5 mL/min/1.73 m² per year)
- Uncertain diagnosis or complex management issues
By understanding and applying this staging system, clinicians can better identify patients at risk for adverse outcomes and implement appropriate interventions to slow disease progression and reduce complications.