What are the chronic kidney disease (CKD) stages based on estimated glomerular filtration rate (eGFR)?

CKD Classification Based on GFR

Chronic kidney disease is classified into five stages (G1–G5) based on estimated glomerular filtration rate, with Stage 3 subdivided into 3a and 3b, and complete staging requires integration of both GFR category and albuminuria level using the KDIGO CGA (Cause-GFR-Albuminuria) classification system. 1

GFR Categories (G Stages)

The KDIGO guideline defines six GFR categories that form the foundation of CKD staging: 1

• Stage G1 (≥90 mL/min/1.73 m²) – Normal or high kidney function. CKD diagnosis requires documented evidence of kidney damage (albuminuria ≥30 mg/g, structural abnormalities on imaging, abnormal urinary sediment, or biopsy-proven disease) persisting for at least 3 months. 1

• Stage G2 (60–89 mL/min/1.73 m²) – Mildly decreased function. Like G1, CKD diagnosis mandates evidence of kidney damage in addition to the GFR value; GFR alone is insufficient. 1

• Stage G3a (45–59 mL/min/1.73 m²) – Mild-to-moderate decrease in kidney function. This stage can be diagnosed by GFR alone without requiring additional markers of kidney damage. 1

• Stage G3b (30–44 mL/min/1.73 m²) – Moderate-to-severe decrease. The subdivision of Stage 3 into 3a and 3b is driven by data demonstrating significantly different mortality, cardiovascular risk, and CKD progression profiles between these GFR ranges. 1

• Stage G4 (15–29 mL/min/1.73 m²) – Severe decrease in kidney function. Patients require intensive management of complications and preparation for possible kidney replacement therapy. 1

• Stage G5 (<15 mL/min/1.73 m²) – Kidney failure. Kidney replacement therapy (dialysis or transplantation) is indicated if uremic symptoms develop. 1

• Stage G5D – The "D" suffix specifically denotes patients with kidney failure who are receiving dialysis therapy. 1

Critical Diagnostic Requirements

All abnormalities must persist for at least 3 months to distinguish chronic from acute kidney disease. 1 This chronicity requirement prevents misclassification of acute kidney injury as CKD and is verified by: 1

• Reviewing historical eGFR or creatinine measurements
• Documenting persistent albuminuria on repeat testing
• Identifying structural abnormalities on imaging (reduced kidney size, cortical thinning)
• Repeating measurements at intervals spanning the 3-month threshold

Complete CGA Classification System

Never stage CKD by GFR alone—the KDIGO guideline mandates complete CGA notation that includes: 1

Cause (C)

The underlying etiology based on systemic disease and anatomic location of pathology (e.g., diabetic kidney disease, hypertensive nephrosclerosis, glomerulonephritis, polycystic kidney disease). 1

Albuminuria Categories (A)

• A1 (<30 mg/g) – Normal to mildly increased albuminuria 1
• A2 (30–300 mg/g) – Moderately increased albuminuria (formerly "microalbuminuria") 1
• A3 (>300 mg/g) – Severely increased albuminuria, including nephrotic-range proteinuria 1

The 30 mg/g threshold represents more than 3 times the normal value in young adults and independently predicts increased risk for CKD complications, cardiovascular mortality, and progression to kidney failure. 1

Combined Risk Stratification (KDIGO Heat Map)

The KDIGO heat map integrates GFR and albuminuria to assign prognostic risk levels that guide monitoring frequency and treatment intensity: 1

• Low risk (green) – G1–G2 with A1. If no other kidney disease markers are present, CKD is not diagnosed. 1

• Moderately increased risk (yellow) – G1–G2 with A2, or G3a with A1. These patients require monitoring 2 times per year. 1

• High risk (orange) – G1–G2 with A3, G3a with A2, or G3b with A1. These combinations warrant monitoring 3 times per year. 1

• Very high risk (red) – G3a with A3, G3b with A2–A3, or any G4–G5 (regardless of albuminuria level). These patients have the highest risk of progression, cardiovascular events, and mortality, requiring monitoring 4 times per year and nephrology referral. 1

GFR Estimation Method

Use the CKD-EPI creatinine equation as the first-line method for eGFR calculation because it demonstrates less bias than the MDRD equation, particularly when eGFR ≥60 mL/min/1.73 m², with improved precision and greater accuracy. 1 When creatinine-based eGFR is uncertain or precise staging is required for clinical decisions, confirm with cystatin C-based or combined creatinine-cystatin C equations. 1

Clinical laboratories must employ creatinine assays calibrated to isotope-dilution mass spectrometry (IDMS) reference methods to minimize systematic bias. 1

Common Pitfalls to Avoid

• Do not diagnose CKD based on a single abnormal eGFR measurement—chronicity requires documentation over at least 3 months. 1

• Do not diagnose Stages 1 or 2 CKD without documented kidney damage—an eGFR of 70 mL/min/1.73 m² with no albuminuria, imaging abnormalities, or other markers does not meet CKD criteria. 1

• Do not rely on serum creatinine alone—always calculate eGFR using validated equations that account for age, sex, and race. 1

• Do not skip albuminuria testing—eGFR and UACR provide independent prognostic information for cardiovascular events, CKD progression, and mortality. 1

• Do not use incomplete staging notation—always report the full CGA classification (e.g., "CKD G3b A2 due to diabetes") rather than GFR category alone. 1