Chronic Kidney Disease Stages
Chronic kidney disease is classified into five stages based on glomerular filtration rate (GFR), with abnormalities of kidney structure or function present for more than 3 months, and should be further categorized by cause and albuminuria level for complete risk stratification. 1, 2
CKD Stage Definitions
Stage 1: GFR ≥90 mL/min/1.73 m²
- Requires evidence of kidney damage (such as albuminuria, proteinuria, or structural abnormalities on imaging) to meet CKD criteria, as GFR alone is insufficient for diagnosis at this level 1, 2
- Management focuses on diagnosis and treatment of underlying conditions, slowing progression, and cardiovascular disease risk reduction 3
Stage 2: GFR 60-89 mL/min/1.73 m²
- Requires evidence of kidney damage for CKD diagnosis, similar to Stage 1 1, 2
- Clinical action emphasizes estimating the rate of disease progression 3
Stage 3: GFR 30-59 mL/min/1.73 m²
- Subdivided into Stage 3a (GFR 45-59 mL/min/1.73 m²) and Stage 3b (GFR 30-44 mL/min/1.73 m²) based on significantly different mortality and cardiovascular risk profiles between these ranges 1, 2
- Can be diagnosed based on GFR alone without requiring additional evidence of kidney damage 2
- Begin evaluation and treatment of complications, as the risk of hypertension, anemia, and hyperphosphatemia increases significantly below GFR 60 2, 3
- All patients with Stage 3b should be referred to nephrology for co-management 3
Stage 4: GFR 15-29 mL/min/1.73 m²
- Represents severe decrease in kidney function with loss of more than half of normal adult kidney function 2, 4
- Mandatory referral to nephrology for intensive management of complications and preparation for kidney replacement therapy 3, 5
- Hypertension prevalence approaches 80% at this stage 2
- Multiple complications become substantially more prevalent when GFR falls below 30 2, 4
Stage 5: GFR <15 mL/min/1.73 m² or on dialysis
- Represents kidney failure with loss of approximately 90% or more of normal kidney function 4
- Accompanied in most cases by signs and symptoms of uremia 4
- Kidney replacement therapy (dialysis or transplantation) is initiated if uremic symptoms develop 2, 3
Complete CKD Classification System (CGA)
The KDIGO guideline recommends classifying CKD based on three components: Cause, GFR category, and Albuminuria category (CGA classification), not GFR alone. 1, 2
Albuminuria Categories
- A1: Normal to mildly increased albuminuria 2
- A2: Moderately increased albuminuria 2
- A3: Severely increased albuminuria (≥300 mg per 24 hours) 2, 6
- An albuminuria level of 30 mg/g represents more than 3 times the normal value and independently predicts increased risk for CKD complications, cardiovascular mortality, and progression to kidney failure 2
Critical Diagnostic Requirements
Duration Criterion
- All abnormalities must persist for at least 3 months to distinguish chronic from acute kidney disease 1, 3, 6
GFR Estimation Method
- Use the CKD-EPI equation for reporting estimated GFR in adults from serum creatinine calibrated to isotope-dilution mass spectrometry reference method 2
- The CKD-EPI equation demonstrates less bias than the MDRD equation, especially at GFR ≥60 mL/min/1.73 m², with improved precision and greater accuracy 2
- Account for serum creatinine, age, sex, race, and body size rather than relying on serum creatinine alone 2, 4
Common Pitfalls to Avoid
- Never classify using GFR alone—always use the complete CGA system (Cause, GFR category, Albuminuria category) to avoid incomplete staging and inaccurate risk stratification 2
- Do not dismiss decreased GFR in elderly patients as "normal aging"—decreased GFR remains an independent predictor of adverse outcomes including death and cardiovascular disease regardless of age 3, 4
- Do not overlook albuminuria assessment—the combination of GFR and albuminuria provides superior risk stratification for disease progression and outcomes compared to GFR alone 2, 6
- Be aware that CKD stages can fluctuate in up to 40% of patients, particularly in elderly populations 7