Chronic Kidney Disease Stages
CKD Definition and Classification Framework
CKD is defined as abnormalities of kidney structure or function present for more than 3 months with health implications, and must be classified using the complete CGA system: Cause, GFR category (G1-G5), and Albuminuria category (A1-A3). 1, 2
The classification requires persistence of abnormalities for at least 3 months to distinguish chronic from acute kidney disease. 1, 2
GFR Categories (G Stages)
Stage G1: GFR ≥90 mL/min/1.73 m²
- Requires evidence of kidney damage (albuminuria, proteinuria, or structural abnormalities on imaging) for CKD diagnosis—GFR alone is insufficient. 2, 3
- Without markers of kidney damage, this is not classified as CKD. 1
Stage G2: GFR 60-89 mL/min/1.73 m²
- Requires BOTH mildly decreased GFR AND documented evidence of kidney damage. 2, 3
- Critical pitfall: Never diagnose Stage 2 CKD based on eGFR alone; this could represent acute kidney injury rather than chronic disease. 3
Stage G3a: GFR 45-59 mL/min/1.73 m²
- Represents mild-to-moderate decrease in kidney function. 1, 2
- Can be diagnosed based on GFR alone without additional evidence of kidney damage. 2
- Subdivision from G3b is driven by significantly different mortality and cardiovascular risk profiles. 1, 2
Stage G3b: GFR 30-44 mL/min/1.73 m²
- Represents moderate-to-severe decrease in kidney function. 1, 2
- Associated with substantially higher risk for complications compared to G3a. 1, 2
Stage G4: GFR 15-29 mL/min/1.73 m²
- Severe decrease in kidney function. 2
- Requires intensive management of complications and preparation for possible kidney replacement therapy. 2
Stage G5: GFR <15 mL/min/1.73 m² or dialysis
- Kidney failure requiring kidney replacement therapy (dialysis or transplantation) if uremic symptoms develop. 2
- The suffix "D" denotes dialysis (e.g., CKD G5D). 1
Albuminuria Categories (A Stages)
A1: <30 mg/g (normal to mildly increased)
A2: 30-300 mg/g (moderately increased)
- Also termed microalbuminuria. 3
- Represents more than 3 times the normal value and independently predicts increased risk for CKD complications, cardiovascular mortality, and progression to kidney failure. 1, 2
A3: >300 mg/g (severely increased)
- Severely increased albuminuria. 2
- Further classification into nephrotic range (>2220 mg/g) may be appropriate in specialist centers. 1
Diagnostic requirement: Perform 2-3 measurements over 3-6 months to confirm albuminuria diagnosis, as a single measurement is insufficient. 2, 3
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. 1, 2
The CKD-EPI equation demonstrates:
- Less bias than the MDRD equation, especially at GFR ≥60 mL/min/1.73 m². 1, 2
- Improved precision and greater accuracy across the range of GFRs. 1, 2
- Ability to report numerical values across all GFR ranges, facilitating communication among providers. 1
Important limitation: All GFR estimation formulas underestimate GFR for subnormal renal function (GFR <90 mL/min). 2
Risk Stratification by Combined GFR and Albuminuria
The combination of GFR and albuminuria provides superior risk stratification for disease progression and outcomes compared to either parameter alone. 1, 2
Risk categories:
- Green (low risk): G1-G2 with A1 (no CKD if no other markers of kidney disease). 1
- Yellow (moderately increased risk): G1-G2 with A2, or G3a with A1. 1
- Orange (high risk): G1-G2 with A3, G3a with A2, or G3b with A1-A2. 1
- Red (very high risk): G3a-G5 with A3, or G4-G5 with any albuminuria category. 1
Critical point: There is no correlation between GFR and albuminuria progression, so both parameters must be monitored independently. 2
Stage-Specific Management Strategies
Stages G1-G2 Management
- Focus on early detection, CKD risk reduction, and treating comorbid conditions. 2
- Annual monitoring is appropriate for stable patients. 2
- Initiate antihypertensive therapy if BP ≥130/80 mmHg. 3
- Initiate SGLT2 inhibitor for cardiorenal protection if UACR ≥200 mg/g, regardless of diabetes status. 3
- Restrict dietary protein to 0.8 g/kg/day. 3
- Monitor eGFR and UACR every 6-12 months. 3
Stage G3 Management
- Estimate progression rate and begin evaluation for complications. 2
- Follow-up with biological control 2-4 times per year based on severity. 2
- As GFR decreases below 60 mL/min/1.73 m², risk of complications (hypertension, anemia, hyperphosphatemia) increases significantly. 2
- Consider nonsteroidal mineralocorticoid receptor antagonist (finerenone) if albuminuria persists despite RASi and SGLT2 inhibitor therapy. 3
Stage G4 Management
- Intensive management of complications required. 2
- Preparation for possible kidney replacement therapy. 2
- Hypertension prevalence approaches 80% at this stage. 2
- Anemia becomes more prevalent. 2
Stage G5 Management
- Kidney replacement therapy (dialysis or transplantation) indicated if uremic symptoms develop. 2
- Preservation of residual GFR is of great importance even at very low levels. 4
Common Complications by Stage
Below GFR 60 mL/min/1.73 m²:
- Increased risk for drug toxicity, endocrine and metabolic complications, cardiovascular disease, and death. 1
- These associations are relevant regardless of country, age, or cause. 1
Below GFR 30 mL/min/1.73 m²:
- Likelihood of having multiple complications increases substantially. 2
- Infection, impaired cognitive and physical function, and threats to patient safety become more common. 1
Critical Diagnostic Pitfalls to Avoid
Never diagnose CKD based on a single abnormal eGFR measurement—this could represent acute kidney injury. 3
Never use GFR alone for staging—always include cause and albuminuria category (complete CGA classification). 1, 2
Never diagnose Stages 1-2 CKD without documented kidney damage—elevated GFR alone is insufficient. 2, 3
Never rely on serum creatinine alone—always use prediction equations accounting for age, sex, race, and body size. 1, 2
Avoid nephrotoxic medications including aminoglycosides, tetracyclines, NSAIDs, and bisphosphonates. 3, 5