What is the classification of nephropathy based on creatinine levels and Glomerular Filtration Rate (GFR)?

Classification of Nephropathy Based on Creatinine and GFR

Chronic kidney disease (CKD) is classified into five distinct stages based on glomerular filtration rate (GFR), with decreasing GFR values indicating progressive loss of kidney function, and additional categorization by albuminuria level.1

GFR Categories for CKD Classification

• Stage 1 CKD: GFR ≥90 mL/min/1.73 m² with evidence of kidney damage (such as albuminuria, proteinuria, or structural abnormalities) 1, 2
• Stage 2 CKD: GFR 60-89 mL/min/1.73 m² with evidence of kidney damage 1, 2
• Stage 3 CKD: GFR 30-59 mL/min/1.73 m², subdivided into:
  • Stage 3a: GFR 45-59 mL/min/1.73 m² 1, 2
  • Stage 3b: GFR 30-44 mL/min/1.73 m² 1, 2
• Stage 4 CKD: GFR 15-29 mL/min/1.73 m², indicating severely reduced kidney function 1, 2
• Stage 5 CKD: GFR <15 mL/min/1.73 m² or dialysis, indicating kidney failure 1, 2

Albuminuria Categories

The KDIGO classification also includes albuminuria categories that should be assessed alongside GFR 2:

• A1: Normal to mildly increased albuminuria (ACR <30 mg/g) 2
• A2: Moderately increased albuminuria (ACR 30-300 mg/g) 2
• A3: Severely increased albuminuria (ACR >300 mg/g) 2

CKD Risk Categories

Risk stratification combines both GFR and albuminuria levels 2:

• Low risk: G1A1, G2A1 (green) 2
• Moderately high risk: G1A2, G2A2, G3aA1 (yellow) 2
• High risk: G1A3, G2A3, G3aA2, G3bA1 (orange) 2
• Very high risk: G3aA3, G3bA2, G3bA3, G4A1, G4A2, G4A3, G5A1, G5A2, G5A3 (red) 2

Diagnostic Considerations

• GFR should be estimated using prediction equations that account for serum creatinine concentration, age, sex, race, and body size, rather than relying on serum creatinine alone 2, 3
• The MDRD Study equation and CKD-EPI equations are recommended for adults, while the Schwartz formula and Counahan-Barratt equation are recommended for children 2
• Serum creatinine alone is an inadequate measure of kidney function as patients may maintain seemingly normal creatinine levels despite declining GFRs 2
• Abnormal GFR or kidney damage must persist for at least 3 months for an accurate diagnosis of CKD 1, 4

Clinical Implications by CKD Stage

• Stages 1-2: Focus on early detection, CKD risk reduction, and treating comorbid conditions 1
• Stage 3: Estimate progression rate and begin evaluation for complications 1
• Stage 4: Intensive management of complications and preparation for kidney replacement therapy 1
• Stage 5: May require kidney replacement therapy (dialysis or transplantation) if uremic symptoms develop 1

Important Clinical Considerations

• The prevalence of complications increases significantly as GFR decreases below 60 mL/min/1.73 m² 1
• At the same serum creatinine level, estimated GFR can vary widely between patients due to differences in age, sex, race, and body size 3
• For a serum creatinine of 100 μmol/L, mean eGFR can range from 31.0-192.8 ml/min using different formulas, highlighting the importance of using standardized GFR estimation 3
• Women and elderly patients (>65 years) with seemingly normal creatinine levels may already have significant reductions in GFR 3

Caveat

• The cause of CKD should be considered when assessing prognosis, as surgical nephron loss (CKD-S) may have a lower likelihood of progression compared to CKD due to medical causes 5
• The KDIGO classification recommends noting kidney disease treatment by dialysis and transplantation when categorizing patients 4