From the Guidelines
Chronic Kidney Disease (CKD) is classified based on cause, GFR category, and albuminuria category (CGA), with GFR categorized into five stages (G1-G5) and albuminuria categorized into three levels (A1-A3) 1. The classification system for CKD is as follows:
- GFR categories:
- G1: Normal or high (≥90 mL/min/1.73m²)
- G2: Mildly decreased (60-89 mL/min/1.73m²)
- G3a: Mildly to moderately decreased (45-59 mL/min/1.73m²)
- G3b: Moderately to severely decreased (30-44 mL/min/1.73m²)
- G4: Severely decreased (15-29 mL/min/1.73m²)
- G5: Kidney failure (<15 mL/min/1.73m²)
- Albuminuria categories:
- A1: Normal to mildly increased (<30 mg/g)
- A2: Moderately increased (30-300 mg/g)
- A3: Severely increased (>300 mg/g) This dual classification system helps guide treatment decisions, as both decreased eGFR and increased albuminuria independently predict progression to kidney failure and cardiovascular complications 1. The KDIGO clinical practice guideline recommends using the CGA classification system to evaluate and manage CKD, which takes into account the cause of CKD, GFR category, and albuminuria category 1. Regular monitoring of both GFR and albuminuria is essential for proper CKD management and risk stratification, with the frequency of visits and referral to nephrology depending on the risk category 1.
From the Research
Classifications of Chronic Kidney Disease (CKD)
The classifications of Chronic Kidney Disease (CKD) can be understood through various studies, including 2, 3, 4, 5, 6.
- The CKD stages are represented by G (for GFR) categories (G1-5) which have the same eGFR thresholds as previous CKD guidelines, as stated in 2.
- The urinary albumin:creatinine ratio (ACR) category is denoted as A (for albuminuria) with three categories: A1, A2 or A3, as mentioned in 2.
- Combining GFR and albuminuria to classify CKD improves prediction of ESRD, according to 4.
- The CGA-classification system proposed by KDIGO provides a semi-quantitative assessment of risks, as stated in 5.
- The CKD classification system includes:
- G1: Normal or high eGFR (>90 ml/min/1.73m2)
- G2: Mildly decreased eGFR (60-89 ml/min/1.73m2)
- G3: Moderately decreased eGFR (30-59 ml/min/1.73m2)
- G4: Severely decreased eGFR (15-29 ml/min/1.73m2)
- G5: Kidney failure (eGFR <15 ml/min/1.73m2 or on dialysis)
- A1: Normal to mildly increased albuminuria (<30 mg/g)
- A2: Moderately increased albuminuria (30-300 mg/g)
- A3: Severely increased albuminuria (>300 mg/g), as mentioned in 2, 5, 6.
CKD Staging
CKD staging stratifies patients in five stages of risk for progressive renal disease based on estimated glomerular filtration rate (eGFR) by formulas and albuminuria, as stated in 3.
- The reliability of formulas to reflect real renal function is a matter of debate, according to 3.
- Misclassification was a constant for all 61 formulas evaluated and averaged 50% for creatinine-based and 35% for cystatin C-based equations, as mentioned in 3.
Risk Assessment
Assessing the risk of adverse outcomes associated with CKD is important for physicians and affected patients alike, as stated in 5.
- The "Tangri"-formula provides a means to quantify the risk of progression for patients with CKD stage G3a-G5 (eGFR 10 - 59 ml/min/1.73 m2) to kidney failure requiring kidney replacement therapy, according to 5.
- Models recently developed by the CKD-prognosis consortium can be used to predict the risk of kidney failure, cardiovascular disease events, and death in patients with advanced CKD, as mentioned in 5.