CKD Stages Based on eGFR
Chronic kidney disease is classified into five stages based on estimated glomerular filtration rate (eGFR), with Stage 1 (≥90 mL/min/1.73 m²) requiring evidence of kidney damage, Stage 2 (60-89 mL/min/1.73 m²) showing mild decrease with kidney damage, Stage 3 (30-59 mL/min/1.73 m²) indicating moderate decrease, Stage 4 (15-29 mL/min/1.73 m²) representing severe decrease, and Stage 5 (<15 mL/min/1.73 m² or dialysis) defining kidney failure. 1, 2, 3
The Five-Stage Classification System
The K/DOQI and KDIGO guidelines established a standardized staging system that has become the international standard:
Stage 1: eGFR ≥90 mL/min/1.73 m²
- Requires evidence of kidney damage (albuminuria, proteinuria, hematuria, or imaging abnormalities)
- Normal or increased GFR with structural kidney abnormalities
- Focus: Diagnose cause, evaluate and treat risk factors 1, 4, 2
Stage 2: eGFR 60-89 mL/min/1.73 m²
- Mild decrease in GFR with evidence of kidney damage
- Must have markers of kidney damage (typically UACR ≥30 mg/g)
- Focus: Control dyslipidemia and cardiovascular risk factors 1, 4, 2
Stage 3: eGFR 30-59 mL/min/1.73 m²
- Moderate decrease in GFR (with or without kidney damage)
- Often subdivided into:
- Stage 3a: 45-59 mL/min/1.73 m²
- Stage 3b: 30-44 mL/min/1.73 m² 5
- Focus: Evaluate and treat CKD complications (anemia, bone metabolism), prepare for potential progression 4
Stage 4: eGFR 15-29 mL/min/1.73 m²
- Severe decrease in GFR (with or without kidney damage)
- Pre-end-stage renal disease
- Focus: Prepare for renal replacement therapy, manage uremic symptoms 1, 4, 2
Stage 5: eGFR <15 mL/min/1.73 m² or dialysis
- Kidney failure requiring or approaching need for dialysis or transplantation
- Some patients may need kidney replacement therapy even with eGFR 15-29 mL/min/1.73 m² due to uremic symptoms 1
- Focus: Dialysis adequacy, transplantation evaluation 4
Critical Diagnostic Requirements
For Stages 1 and 2: Evidence of kidney damage is mandatory. This includes:
- Albuminuria (UACR ≥30 mg/g)
- Proteinuria or hematuria
- Pathological abnormalities
- Radiographic imaging abnormalities 1, 2
For Stages 3-5: Reduced eGFR alone is sufficient for diagnosis, regardless of whether kidney damage markers are present 1, 3
Temporal Component
All CKD diagnoses require abnormalities persisting for at least 3 months to distinguish from acute kidney injury or acute kidney disease 3, 6. This can be established through:
- Review of past GFR measurements
- Review of past albuminuria/proteinuria results
- Imaging showing reduced kidney size or cortical thinning
- Pathological findings of fibrosis and atrophy
- Repeat measurements within and beyond the 3-month timepoint 6
Important Clinical Caveats
Do not assume chronicity from a single abnormal measurement, as this could represent acute kidney injury rather than CKD 6. However, if CKD is deemed likely based on clinical context, initiation of CKD-specific treatments can begin at first presentation 6.
The 2024 KDIGO guidelines now recommend using combined creatinine and cystatin C equations for more accurate eGFR estimation when cystatin C is available 7, 6. The staging system remains fundamentally unchanged but incorporates albuminuria categories (A1: <30 mg/g, A2: 30-300 mg/g, A3: >300 mg/g) for comprehensive risk stratification 2.
This classification system has become one of the most impactful developments in nephrology, replacing vague terminology like "chronic renal insufficiency" or "pre-dialysis" with precise, internationally standardized staging 3.