How do you stage Chronic Kidney Disease (CKD)?

How to Stage Chronic Kidney Disease

CKD is staged using a two-dimensional classification system that combines GFR categories (G1-G5) with albuminuria categories (A1-A3), creating a risk stratification matrix that guides prognosis and management decisions. 1

GFR Categories (G Stages)

The five GFR stages are defined by estimated glomerular filtration rate (eGFR) in mL/min/1.73 m²: 1, 2, 3

• G1 (Normal or high): eGFR ≥90 mL/min/1.73 m² 1
• G2 (Mildly decreased): eGFR 60-89 mL/min/1.73 m² 1
• G3a (Mildly to moderately decreased): eGFR 45-59 mL/min/1.73 m² 1
• G3b (Moderately to severely decreased): eGFR 30-44 mL/min/1.73 m² 1
• G4 (Severely decreased): eGFR 15-29 mL/min/1.73 m² 1
• G5 (Kidney failure): eGFR <15 mL/min/1.73 m² 1

Calculating eGFR

Use the CKD-EPI equation to estimate GFR, which is preferred over the MDRD equation. 3 The CKD-EPI equation provides more accurate estimates, particularly in younger individuals and those with higher GFR values. 4

For initial GFR assessment, measure serum creatinine and calculate eGFR using the CKD-EPI 2009 equation. 4 If confirmation is needed due to extremes of muscle mass, dietary factors, or assay interference, measure cystatin C and calculate eGFR using cystatin C-based equations (eGFRcys or eGFRcr-cys), or directly measure GFR using clearance procedures. 4

Albuminuria Categories (A Stages)

Albuminuria is measured using urine albumin-to-creatinine ratio (UACR) from a spot urine sample: 1, 3

• A1 (Normal to mildly increased): UACR <30 mg/g creatinine 1
• A2 (Moderately increased): UACR 30-299 mg/g creatinine 1
• A3 (Severely increased): UACR ≥300 mg/g creatinine 1

Measure urine albumin and creatinine in an untimed spot urine collection and report the albumin-to-creatinine ratio. 4 If confirmation is required due to diurnal variation or conditions affecting creatinine excretion, measure albumin excretion rate from a timed urine collection. 4

Critical Diagnostic Requirements

For stages G1 and G2, CKD cannot be diagnosed by eGFR alone—there must be evidence of kidney damage (albuminuria, imaging abnormalities, or biopsy findings) present for >3 months. 1 This is a common pitfall: an eGFR of 70 mL/min/1.73 m² without any markers of kidney damage does not constitute CKD.

For stages G3-G5, an eGFR <60 mL/min/1.73 m² persisting for >3 months is sufficient to diagnose CKD, even without albuminuria. 1 The definition requires abnormalities to persist for at least 3 months to distinguish CKD from acute kidney injury. 3, 5

Risk Stratification Using the CGA Matrix

The combination of GFR and albuminuria categories creates a color-coded risk matrix for CKD progression and adverse outcomes: 1

• Green (Low risk): G1A1, G2A1 1
• Yellow (Moderately high risk): G1A2, G2A2, G3aA1 1
• Orange (High risk): G1A3, G2A3, G3aA2, G3bA1 1
• Red (Very high risk): G3aA3, G3bA2, G3bA3, G4A1, G4A2, G4A3 1
• Dark red (Highest risk): G5A1, G5A2, G5A3 1

This matrix guides monitoring frequency, treatment intensity, and nephrology referral decisions. 1

Monitoring Frequency

Both eGFR and albuminuria should be monitored at least annually to detect CKD, monitor progression, and guide medication dosing. 3 More frequent monitoring is warranted for patients at higher risk categories or those with rapidly declining kidney function. 2

Nephrology Referral Thresholds

Refer to nephrology when: 1

• eGFR <30 mL/min/1.73 m² (stages G4-G5) regardless of albuminuria 1
• Any stage with A3 albuminuria (≥300 mg/g) 1
• Rapidly declining eGFR or rapidly increasing albuminuria 1
• Active urinary sediment or nephrotic syndrome 1
• Absence of retinopathy in type 1 diabetes (suggests non-diabetic kidney disease) 1