What are the stages of Chronic Kidney Disease (CKD)?

Stages of Chronic Kidney Disease (CKD)

Chronic Kidney Disease is classified into five stages based primarily on glomerular filtration rate (GFR), with additional consideration for albuminuria and cause of kidney disease.

CKD Definition and Classification

• CKD is defined as either kidney damage or decreased kidney function (GFR < 60 mL/min/1.73 m²) persisting for 3 or more months 1
• Kidney damage is usually ascertained by markers such as persistent proteinuria, abnormalities in urine sediment, blood and urine chemistry measurements, or abnormal findings on imaging studies 1
• The National Kidney Foundation Kidney Disease Outcomes Quality Initiative (K/DOQI) classification system is the standard for staging CKD 1

The Five Stages of CKD

Stage 1

• GFR ≥ 90 mL/min/1.73 m² with evidence of kidney damage 1
• Normal or high kidney function but with signs of kidney damage (e.g., albuminuria, urinary sediment abnormalities) 1, 2
• Clinical action plan: Diagnosis and treatment of underlying conditions, slowing progression, and cardiovascular disease risk reduction 1

Stage 2

• GFR 60-89 mL/min/1.73 m² with evidence of kidney damage 1, 3
• Mildly decreased kidney function with signs of kidney damage 1
• Clinical action plan: Estimating progression of kidney disease 1, 3

Stage 3

• GFR 30-59 mL/min/1.73 m² 1
• Often subdivided into:
  • Stage 3a: GFR 45-59 mL/min/1.73 m² (mildly to moderately decreased) 1
  • Stage 3b: GFR 30-44 mL/min/1.73 m² (moderately to severely decreased) 1
• Clinical action plan: Evaluation and treatment of complications (anemia, malnutrition, bone disease, neuropathy, decreased quality of life) 1

Stage 4

• GFR 15-29 mL/min/1.73 m² (severely decreased) 1
• Clinical action plan: Preparation for kidney replacement therapy 1
• Referral to nephrologist is strongly recommended at this stage 1, 4

Stage 5

• GFR < 15 mL/min/1.73 m² or kidney failure requiring dialysis 1
• Also defined as kidney failure with either GFR < 15 mL/min/1.73 m² or need for kidney replacement therapy (dialysis or transplantation) 1
• Clinical action plan: Kidney replacement therapy if uremia is present 1

Albuminuria Classification

• Albuminuria is an important marker of kidney damage and should be considered alongside GFR for comprehensive CKD staging 1, 5
• Categories of albuminuria based on urine albumin-to-creatinine ratio (UACR):
  • A1: Normal to mildly increased (< 30 mg/g) 1
  • A2: Moderately increased (30-299 mg/g) 1
  • A3: Severely increased (≥ 300 mg/g) 1

Clinical Implications and Management

• Patients with CKD stage 4 (GFR < 30 mL/min/1.73 m²) should be referred to a nephrologist for consultation and co-management 1
• The risk of complications increases significantly below GFR of 60 mL/min/1.73 m² 1, 5
• Treatment goals include slowing progression, managing complications, and preparing for kidney replacement therapy when necessary 1, 6
• Early detection and intervention can significantly improve outcomes and reduce mortality 5, 7
• The prevalence of early stages of CKD (stages 1-4) is more than 100 times greater than kidney failure (stage 5) 1

Important Considerations

• Age-related decline in GFR should not be considered "normal aging" as decreased GFR in the elderly remains an independent predictor of adverse outcomes 1
• Kidney failure (stage 5) is not synonymous with end-stage renal disease (ESRD), which is an administrative term indicating treatment with dialysis or transplantation 1
• Comprehensive CKD management requires addressing cardiovascular risk factors, which are major contributors to mortality in CKD patients 5, 6
• Multidisciplinary care involving primary care providers and specialists improves outcomes in CKD management 4, 7