Chronic Kidney Disease Staging Based on Glomerular Filtration Rate
Chronic kidney disease (CKD) is classified into five distinct stages based on glomerular filtration rate (GFR), with decreasing GFR values indicating progressive loss of kidney function. 1
CKD Stages Based on GFR
- Stage 1: GFR ≥ 90 mL/min/1.73 m² with evidence of kidney damage (such as albuminuria, proteinuria, or structural abnormalities) 1, 2
- Stage 2: GFR 60-89 mL/min/1.73 m² with evidence of kidney damage 1, 2
- Stage 3: GFR 30-59 mL/min/1.73 m², further divided into:
- Stage 4: GFR 15-29 mL/min/1.73 m² 1, 2
- Stage 5: GFR < 15 mL/min/1.73 m² or requiring dialysis 1, 2
Important Diagnostic Considerations
- CKD is defined as abnormalities in kidney structure or function present for more than 3 months with health implications 3
- For stages 1 and 2, evidence of kidney damage (such as albuminuria) is required for CKD diagnosis, while stages 3-5 can be diagnosed based on GFR alone 1, 2
- GFR should be estimated using prediction equations that account for serum creatinine, age, sex, race, and body size, rather than relying on serum creatinine alone 1, 4
- Common equations include the Modification of Diet in Renal Disease (MDRD) Study equation and CKD Epidemiology Collaboration (CKD-EPI) equation 4, 5
Clinical Significance by Stage
- Stages 1-2: Focus on early detection, CKD risk reduction, and treating comorbid conditions 1, 2
- Stage 3: Begin evaluation for complications and estimate progression rate 1, 2
- Stage 4: Intensive management of complications and preparation for possible kidney replacement therapy 1, 2
- Stage 5: Consider kidney replacement therapy (dialysis or transplantation) if uremic symptoms develop 1, 2, 6
Risk Stratification and Albuminuria
- CKD classification should include albuminuria categories alongside GFR 3, 2:
- A1: Normal to mildly increased albuminuria
- A2: Moderately increased albuminuria
- A3: Severely increased albuminuria 1
- The combination of GFR and albuminuria provides better risk stratification for disease progression and outcomes 3, 1
- The risk of complications increases significantly when GFR falls below 60 mL/min/1.73 m² 1, 2
Clinical Complications by CKD Stage
- As GFR decreases below 60 mL/min/1.73 m², the risk of complications such as hypertension, anemia, and hyperphosphatemia increases significantly 1
- The prevalence of hypertension approaches 80% in patients with stage 4 CKD 1
- Anemia becomes more prevalent as GFR falls below 60 mL/min/1.73 m² 1
- Multiple complications become substantially more likely when GFR falls below 30 mL/min/1.73 m² 1
Common Pitfalls in CKD Staging
- Relying solely on serum creatinine without calculating estimated GFR can lead to missed diagnoses, especially in elderly patients or those with reduced muscle mass 4, 7
- Failing to recognize that age-related decline in GFR should not be considered "normal aging" as decreased GFR in the elderly remains an independent predictor of adverse outcomes 2
- Not considering both GFR and albuminuria when assessing CKD severity and prognosis 3, 5
- Overlooking the need for nephrology referral for patients with CKD stage 4 (GFR < 30 mL/min/1.73 m²) 2