What are the criteria for staging kidney disease based on glomerular filtration rate (GFR)?

Staging Kidney Disease Based on Glomerular Filtration Rate (GFR)

Chronic kidney disease (CKD) is staged primarily using glomerular filtration rate (GFR) values, with Stage 1 being GFR ≥90 mL/min/1.73m² with kidney damage, and Stage 5 being GFR <15 mL/min/1.73m² or kidney failure requiring replacement therapy. 1

GFR-Based CKD Staging Criteria

The National Kidney Foundation Kidney Disease Outcomes Quality Initiative (K/DOQI) classification system defines the following stages based on GFR:

Stage	Description	GFR (mL/min/1.73m²)
1	Kidney damage with normal or increased GFR	≥90
2	Kidney damage with mild decrease in GFR	60-89
3	Moderate decrease in GFR	30-59
4	Severe decrease in GFR	15-29
5	Kidney failure	<15 or dialysis

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Key Elements of CKD Definition and Staging

1. Chronicity Requirement: CKD is defined as either kidney damage or decreased GFR for 3 or more months 1

2. Kidney Damage Markers (especially important for Stages 1-2):

   • Persistent proteinuria/albuminuria (primary marker)
   • Abnormalities in urine sediment
   • Abnormal blood/urine chemistry
   • Abnormal imaging findings 1

3. GFR Measurement Methods:

   • Recommended approach: Use creatinine-based estimated GFR (eGFRcr) for initial assessment
   • If available, use combined creatinine and cystatin C-based estimation (eGFRcr-cys) for more accurate assessment 1

Clinical Implications of GFR Staging

• GFR <60 mL/min/1.73m² (Stage 3 or higher): Represents loss of half or more of normal kidney function and is associated with increased complications 1

• GFR <15 mL/min/1.73m² (Stage 5): Defines kidney failure, typically accompanied by uremic symptoms and/or need for kidney replacement therapy 1

• Age Considerations: Although GFR naturally declines with age, decreased GFR in elderly patients still predicts adverse outcomes and requires the same staging criteria 1

Important Clinical Considerations

1. Confirming Chronicity: Do not diagnose CKD based on a single abnormal GFR measurement; confirm with:

   • Review of past GFR measurements
   • Imaging findings (reduced kidney size, cortical thinning)
   • Kidney pathology showing fibrosis/atrophy
   • Repeat measurements beyond the 3-month point 1

2. Distinguishing from Acute Kidney Injury: A single abnormal GFR value could represent acute kidney injury rather than CKD 1

3. GFR Estimation Limitations:

   • eGFR may be less accurate in certain populations or clinical situations
   • Consider more accurate GFR measurement methods when clinical decisions depend on precise GFR values 1

Common Pitfalls to Avoid

1. Relying solely on serum creatinine: Creatinine alone without using an estimating equation can be misleading due to variations based on muscle mass, diet, and other factors 1

2. Ignoring albuminuria/proteinuria: CKD staging requires assessment of both GFR and markers of kidney damage 1

3. Misclassifying transient GFR changes: Acute decreases in GFR may not represent CKD; chronicity must be established 1

4. Confusing ESRD with kidney failure: End-Stage Renal Disease (ESRD) is an administrative term for patients receiving dialysis or transplantation, while kidney failure (Stage 5 CKD) is defined by GFR <15 mL/min/1.73m² regardless of treatment status 1

5. Overlooking age-related GFR decline: While GFR naturally decreases with age, this should not be dismissed as "normal aging" when it reaches CKD threshold values 1

By using these GFR-based staging criteria consistently, clinicians can better identify patients at risk for CKD progression and implement appropriate interventions to improve outcomes.