What are the KDIGO classification grades for chronic kidney disease?

KDIGO Classification of Chronic Kidney Disease

Chronic kidney disease is classified using the CGA system: Cause, GFR category (G1-G5), and Albuminuria category (A1-A3), with CKD defined as kidney abnormalities present for >3 months. 1

GFR Categories (G Stages)

The GFR classification divides kidney function into six categories based on estimated glomerular filtration rate in mL/min/1.73 m²: 1, 2

• G1: ≥90 mL/min/1.73 m² (normal or high kidney function, requires evidence of kidney damage for CKD diagnosis) 1, 2
• G2: 60-89 mL/min/1.73 m² (mildly decreased kidney function, requires evidence of kidney damage for CKD diagnosis) 1, 2
• G3a: 45-59 mL/min/1.73 m² (mildly to moderately decreased kidney function) 1, 2
• G3b: 30-44 mL/min/1.73 m² (moderately to severely decreased kidney function) 1, 2
• G4: 15-29 mL/min/1.73 m² (severely decreased kidney function) 1, 2
• G5: <15 mL/min/1.73 m² (kidney failure) 1, 2
• G5D: Kidney failure on dialysis (suffix D denotes dialysis therapy) 1

Albuminuria Categories (A Stages)

Albuminuria is classified into three categories based on albumin-to-creatinine ratio (ACR): 1, 2

• A1: <30 mg/g (<3 mg/mmol) - Normal to mildly increased 1
• A2: 30-300 mg/g (3-30 mg/mmol) - Moderately increased 1
• A3: >300 mg/g (>30 mg/mmol) - Severely increased (includes nephrotic syndrome when albumin excretion >2200 mg/24h) 1

Risk Stratification by Combined GFR and Albuminuria

The KDIGO heat map stratifies prognosis risk using both GFR and albuminuria categories together: 1

Low Risk (Green)

• G1-G2 with A1 (no CKD if no other markers of kidney disease present) 1

Moderately Increased Risk (Yellow)

• G1-G2 with A2 1
• G3a with A1 1

High Risk (Orange)

• G1-G2 with A3 1
• G3a with A2 1
• G3b with A1 1

Very High Risk (Red)

• G3a with A3 1
• G3b with A2-A3 1
• G4-G5 with any albuminuria category 1

Diagnostic Requirements

CKD diagnosis requires abnormalities to persist for at least 3 months to distinguish chronic from acute kidney disease. 1, 2, 3

For stages G1 and G2, evidence of kidney damage is mandatory for CKD diagnosis, including: 1, 2

• Albuminuria (ACR ≥30 mg/g) 1, 2
• Urine sediment abnormalities 1
• Electrolyte abnormalities from tubular disorders 1
• Structural abnormalities on imaging 1
• Histologic abnormalities 1
• History of kidney transplantation 1

For stages G3-G5, GFR <60 mL/min/1.73 m² alone is sufficient for CKD diagnosis without requiring additional markers of kidney damage. 2, 3

GFR Estimation Methods

Use serum creatinine with the CKD-EPI equation for initial GFR assessment, as it demonstrates less bias than the MDRD equation, especially at GFR ≥60 mL/min/1.73 m². 1, 2

Consider cystatin C-based or combined creatinine-cystatin C equations for confirmatory testing when creatinine-based eGFR is less accurate and GFR affects clinical decisions. 1, 3

Clinical laboratories must measure serum creatinine using assays calibrated to international standard reference materials with minimal bias compared to isotope-dilution mass spectrometry. 1

Critical Classification Principles

Always use the complete CGA classification (Cause, GFR category, Albuminuria category), not GFR alone, as this provides incomplete risk stratification and misses critical prognostic information. 2, 3

GFR and albuminuria provide independent prognostic information—there is no correlation between GFR decline and albuminuria progression, so both parameters must be monitored separately. 2, 3

The subdivision of Stage 3 into 3a and 3b reflects significantly different outcomes and risk profiles, particularly regarding cardiovascular mortality, acute kidney injury risk, and CKD progression rates. 2