Chronic Kidney Disease Staging and Management

CKD Staging

• The American Journal of Kidney Diseases recommends classifying chronic kidney disease (CKD) into five distinct stages based on glomerular filtration rate (GFR), with decreasing GFR values indicating progressive loss of kidney function 1, 2
• Stage 1 CKD is characterized by a GFR ≥90 mL/min/1.73 m² with evidence of kidney damage, such as albuminuria, proteinuria, or structural abnormalities 1, 2, 3
• Stage 2 CKD is characterized by a GFR 60-89 mL/min/1.73 m² with evidence of kidney damage 1, 2, 3
• Stage 3 CKD is characterized by a GFR 30-59 mL/min/1.73 m², with a moderate decrease in kidney function, and can be further divided into Stage 3a (GFR 45-59 mL/min/1.73 m²) and Stage 3b (GFR 30-44 mL/min/1.73 m²) 1, 4, 5
• Stage 4 CKD is characterized by a GFR 15-29 mL/min/1.73 m², indicating a severe decrease in kidney function 1, 2, 3
• Stage 5 CKD is characterized by a GFR <15 mL/min/1.73 m² or dialysis, indicating kidney failure 1, 2, 3

Clinical Significance and Management

• The National Kidney Foundation recommends that patients with Stage 1-2 CKD focus on early detection, CKD risk reduction, and treating comorbid conditions 6, 7
• For patients with Stage 3 CKD, the American Journal of Kidney Diseases recommends estimating progression rate and beginning evaluation for complications 6, 7
• Patients with Stage 4 CKD require intensive management of complications and preparation for possible kidney replacement therapy 6, 7
• Patients with Stage 5 CKD may require kidney replacement therapy (dialysis or transplantation) if uremic symptoms develop 6, 7

Diagnostic Considerations

• The American Journal of Kidney Diseases recommends estimating GFR using prediction equations that account for serum creatinine, age, sex, race, and body size, rather than relying on serum creatinine alone 1
• Abnormal GFR or kidney damage must persist for at least 3 months for an accurate diagnosis of CKD 2
• In stages 1 and 2, evidence of kidney damage (such as albuminuria) is required for CKD diagnosis, while stages 3-5 can be diagnosed based on GFR alone 1, 2

Clinical Complications by CKD Stage

• As GFR decreases below 60 mL/min/1.73 m², the risk of complications, such as hypertension, anemia, and hyperphosphatemia, increases significantly 7, 5
• The prevalence of hypertension approaches 80% in patients with stage 4 CKD 7
• Anemia becomes more prevalent as GFR falls below 60 mL/min/1.73 m² 7
• The likelihood of having multiple complications increases substantially when GFR falls below 30 mL/min/1.73 m² 7
• The European Heart Journal recommends that the presence of proteinuria in diabetic patients supports a CKD diagnosis regardless of GFR values 8

Classification of Nephropathy Based on Creatinine and GFR

GFR Categories for CKD Classification

• The National Kidney Foundation recommends estimating GFR using prediction equations that account for serum creatinine concentration, age, sex, race, and body size, rather than relying on serum creatinine alone 9

Albuminuria Categories

• The Kidney Disease: Improving Global Outcomes (KDIGO) classification includes albuminuria categories that should be assessed alongside GFR, with categories including A1 (normal to mildly increased albuminuria), A2 (moderately increased albuminuria), and A3 (severely increased albuminuria) 10

CKD Risk Categories

• The Kidney Disease: Improving Global Outcomes (KDIGO) classification recommends risk stratification combining both GFR and albuminuria levels, with categories including low risk, moderately high risk, high risk, and very high risk 11

Diagnostic Considerations

• The National Kidney Foundation recommends using the MDRD Study equation and CKD-EPI equations for adults, and the Schwartz formula and Counahan-Barratt equation for children to estimate GFR 9

Chronic Kidney Disease Diagnosis and Staging

Diagnostic Considerations

• CKD is defined as abnormalities in kidney structure or function present for more than 3 months with health implications, according to the Annals of Internal Medicine 12
• The combination of GFR and albuminuria provides better risk stratification for disease progression and outcomes, as recommended by the Annals of Internal Medicine 12

Risk Stratification

• CKD classification should include albuminuria categories alongside GFR, as suggested by the Annals of Internal Medicine 12

Chronic Kidney Disease Staging and Management

CKD Classification and Staging

• The American College of Physicians recommends classifying CKD into five stages based on GFR, with Stage 3 subdivided into 3a and 3b, and incorporating both GFR category and albuminuria category (CGA classification) for complete risk stratification 13, 14
• The subdivision of Stage 3 into 3a and 3b is driven by data demonstrating different outcomes and risk profiles between these GFR ranges, particularly regarding cardiovascular mortality, acute kidney injury risk, and CKD progression 13, 14

Diagnostic Requirements and Albuminuria Categories

• An albuminuria level of 30 mg/g 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 13, 14

GFR Estimation Method

• The National Kidney Foundation recommends using the CKD-EPI equation for reporting estimated GFR in adults from serum creatinine calibrated to isotope-dilution mass spectrometry reference method 13, 14
• The CKD-EPI equation demonstrates less bias than the MDRD equation, especially at GFR ≥60 mL/min/1.73 m², with improved precision and greater accuracy 13, 14

Common Pitfalls to Avoid

• The American College of Physicians recommends classifying using the complete CGA system (Cause, GFR category, Albuminuria category), not GFR alone, to avoid incomplete staging 13, 14

Chronic Kidney Disease Classification and Management

CKD Diagnosis and Staging

• The National Kidney Foundation recommends classifying chronic kidney disease into five stages based on glomerular filtration rate (GFR), with abnormalities of kidney structure or function present for more than 3 months, and should be further categorized by cause and albuminuria level for complete risk stratification 15
• The Kidney Disease: Improving Global Outcomes (KDIGO) guideline recommends classifying CKD based on three components: Cause, GFR category, and Albuminuria category (CGA classification), not GFR alone 15

CKD Stage Definitions

• Stage 1 CKD requires evidence of kidney damage, such as albuminuria, proteinuria, or structural abnormalities on imaging, to meet CKD criteria, as GFR alone is insufficient for diagnosis at this level 15
• Stage 3 CKD is subdivided into Stage 3a (GFR 45-59 mL/min/1.73 m²) and Stage 3b (GFR 30-44 mL/min/1.73 m²) based on significantly different mortality and cardiovascular risk profiles between these ranges 15

Critical Diagnostic Requirements

• All abnormalities must persist for at least 3 months to distinguish chronic from acute kidney disease 15

Chronic Kidney Disease Staging and Management

CKD Stages and Management

• Stages 1 and 2 are considered stable and warrant annual monitoring, according to the Anaesthesia guideline society 16
• Stage 3 is subdivided into 3a and 3b based on significantly different mortality and cardiovascular risk profiles, and follow-up with biological control should occur 2-4 times per year based on severity, as recommended by the Anaesthesia guideline society 16
• Stage 5 represents end-stage renal failure or kidney failure, and kidney replacement therapy (dialysis or transplantation) is indicated if uremic symptoms develop, as stated in the Anaesthesia guideline society 16

Diagnostic Requirements and Albuminuria Classification

• Three albuminuria categories exist: A1 (normal to mildly increased, <30 mg/g), A2 (moderately increased, 30-300 mg/g), and A3 (severely increased, >300 mg/g), and measure the albumin-to-creatinine ratio (ACR) on a single urine sample rather than 24-hour urine collection, as recommended by the Anaesthesia guideline society 16
• An albuminuria level of 30 mg/g represents more than 3 times the normal value and independently predicts increased risk for CKD complications, cardiovascular mortality, and progression to kidney failure, and perform at least 2-3 measurements over 6 months to confirm diagnosis, according to the Anaesthesia guideline society 16
• All GFR estimation formulas underestimate GFR for subnormal renal function (GFR <90 mL/min), and there is no correlation between GFR and albuminuria progression, so both parameters must be monitored independently, as stated by the Anaesthesia guideline society 16

KDIGO Classification and Risk Stratification of Chronic Kidney Disease

Definition and Classification

• The KDIGO guideline defines chronic kidney disease (CKD) using the CGA system—Cause, GFR category (G1‑G5), and Albuminuria category (A1‑A3)—and requires that kidney abnormalities persist for more than 3 months to distinguish chronic from acute disease. 17

GFR Categories (G Stages)

• KDIGO categorizes estimated glomerular filtration rate (eGFR) into six stages:

  • G1 ≥ 90 mL/min/1.73 m² (normal/high function)
  • G2 60‑89 mL/min/1.73 m² (mildly decreased)
  • G3a 45‑59 mL/min/1.73 m² (mild‑moderate decrease)
  • G3b 30‑44 mL/min/1.73 m² (moderate‑severe decrease)
  • G4 15‑29 mL/min/1.73 m² (severe decrease)
  • G5 < 15 mL/min/1.73 m² (kidney failure)
  • G5D denotes kidney failure treated with dialysis. 18

• The “D” suffix (G5D) specifically indicates patients receiving dialysis therapy. 19

Albuminuria Categories (A Stages)

• KDIGO classifies albumin‑to‑creatinine ratio (ACR) into three categories:
  
  • A1 < 30 mg/g (normal to mildly increased)
  • A2 30‑300 mg/g (moderately increased)
  • A3 > 300 mg/g (severely increased; includes nephrotic‑range proteinuria). 20

Combined GFR‑Albuminuria Risk Stratification (KDIGO Heat Map)

• KDIGO’s heat‑map integrates GFR and albuminuria categories to assign prognostic risk:

  • Low risk (green) – G1‑G2 with A1; if no other kidney disease markers are present, CKD is not diagnosed. 17

  • Moderately increased risk (yellow) –

    • G1‑G2 with A2
    • G3a with A1

  • High risk (orange) –

    • G1‑G2 with A3
    • G3a with A2
    • G3b with A1

  • Very high risk (red) –

    • G3a with A3
    • G3b with A2‑A3
    • G4‑G5 (any albuminuria level)

Diagnostic Requirements

• CKD diagnosis mandates that the defining abnormality (reduced eGFR or markers of kidney damage) be present for at least 3 months. 18

• For patients in G1‑G2, CKD can be diagnosed only when evidence of kidney damage is documented, which may include any of the following:

  • Albuminuria (ACR ≥ 30 mg/g)
  • Abnormal urine sediment
  • Electrolyte disturbances due to tubular dysfunction
  • Structural abnormalities identified on imaging
  • Histologic abnormalities on kidney biopsy
  • History of kidney transplantation

GFR Estimation Methods

• KDIGO recommends using serum‑creatinine‑based CKD‑EPI equation for initial eGFR estimation because it shows less bias than the MDRD equation, particularly when eGFR ≥ 60 mL/min/1.73 m². 18

• When creatinine‑based eGFR is uncertain or when clinical decisions depend on precise GFR, KDIGO advises confirming with cystatin C‑based or combined creatinine‑cystatin C equations. 18

• Clinical laboratories must employ creatinine assays calibrated to international reference materials and aligned with isotope‑dilution mass spectrometry (IDMS) to minimize systematic bias. 18

KDIGO Guidelines for Chronic Kidney Disease Classification and Staging

Diagnostic Requirements

• CKD is diagnosed only when kidney abnormalities persist for ≥ 3 months, distinguishing chronic from acute disease. This time‑frame is required by the KDIGO guideline. 21
• Evidence of kidney damage may be documented by any of the following on repeat testing over the 3‑month period: albuminuria ≥ 30 mg/g, abnormal renal imaging, abnormal biopsy, or abnormal urinary sediment. 21

The CGA (Cause‑GFR‑Albuminuria) Classification System

Cause (C)

• The underlying etiology is assigned based on systemic disease presence and the anatomic location of renal pathology (glomerular, tubular, vascular, cystic). Common causes include diabetic kidney disease, hypertensive nephrosclerosis, glomerulonephritis, and polycystic kidney disease. 21

GFR Categories (G)

• The KDIGO guideline mandates subdivision of G3 into G3a and G3b because these ranges have markedly different mortality, cardiovascular risk, and progression profiles. 22
• For G1 and G2, CKD cannot be diagnosed on GFR alone; documented kidney damage (e.g., albuminuria, imaging abnormality) is required. An individual with eGFR 55 mL/min/1.73 m² and no other abnormalities does not meet CKD criteria. 22
• Suffixes are added to denote special populations: “D” for dialysis (G5D) and “T” for transplant recipients. 21

Albuminuria Categories (A)

• Albuminuria is measured on a random spot urine sample; the 30 mg/g threshold (≈ 3 × normal) independently predicts CKD complications, cardiovascular mortality, and progression to kidney failure. 23

Combined Risk Stratification (KDIGO Heat Map)

• The KDIGO heat map combines GFR and albuminuria categories to assign a color‑coded risk level that guides clinical management:

• This risk stratification informs monitoring frequency, blood‑pressure targets, timing of nephrology referral, and cardiovascular risk‑reduction strategies per KDIGO recommendations. 23

eGFR Estimation Method

• KDIGO recommends the CKD‑EPI creatinine equation as the first‑line method for eGFR calculation because it shows less bias than the older MDRD equation, especially when eGFR ≥ 60 mL/min/1.73 m². 22
• When creatinine‑based eGFR is uncertain or precise staging is required, KDIGO advises confirming with cystatin C‑based or combined creatinine‑cystatin C equations.

Practical Classification Rules

• Never stage CKD by GFR alone; always report the full CGA notation (e.g., “CKD G3b A2 due to diabetes”). This complete classification is required for accurate risk stratification and appropriate management. [23][22]
• Do not diagnose CKD on a single abnormal test; the abnormality must be documented on at least two occasions ≥ 3 months apart to satisfy the chronicity criterion. 21

All statements are derived from KDIGO clinical practice guidelines and are supported by the cited peer‑reviewed sources.

KDIGO Chronic Kidney Disease Staging and Management

GFR Category Definitions

• G1 (≥90 mL/min/1.73 m²) – considered normal or high kidney function; used as the reference range for eGFR reporting. 24
• Stage 3 subdivision – G3a (45–59 mL/min/1.73 m²) and G3b (30–44 mL/min/1.73 m²) are distinguished because the lower GFR range (30–44) is associated with markedly higher mortality, cardiovascular risk, and faster CKD progression. 25
• Dialysis designation – Patients on chronic dialysis are classified as G5D to separate them from non‑dialyzed patients with eGFR < 15 mL/min/1.73 m²; kidney transplant recipients receive a “T” suffix. 25

Albuminuria Category Definitions

• Spot urine sampling – A random spot urine specimen for ACR is preferred over 24‑hour collections because it is less burdensome and provides equivalent predictive value for CKD outcomes. 26
• Confirmation of persistent albuminuria – Abnormal ACR values must be documented on at least two of three specimens collected over 3–6 months to account for biological variability. 26

Diagnostic Criteria for CKD

• G1–G2 – CKD diagnosis requires evidence of kidney damage in addition to eGFR (e.g., albuminuria ≥30 mg/g, abnormal urine sediment, tubular electrolyte disturbances, histologic abnormalities on biopsy, or a history of kidney transplantation). 26, 25, 24
• G3–G5 – CKD can be diagnosed on the basis of reduced eGFR alone, with or without additional markers of kidney damage. 24

Combined Risk Stratification (KDIGO Heat Map)

• Low risk (Green) – G1–G2 with A1. 25
• Moderately increased risk (Yellow) – G1–G2 with A2. 25
• High risk (Orange) – G1–G2 with A3. 25
• Very high risk (Red) – G3b with A2 or A3; any patient with G4–G5 regardless of albuminuria level. 25

CKD Notation and Reporting

• The full CGA notation (Cause, GFR category, Albuminuria category) must be used when documenting CKD to ensure accurate risk stratification and guide management decisions (e.g., “CKD G3b A2 due to diabetes”). 25

Stage‑Specific Management Priorities