What are the different stages of Chronic Kidney Disease (CKD) and does albuminuria affect the staging?

From the Guidelines

Chronic Kidney Disease (CKD) is classified into five stages based primarily on estimated glomerular filtration rate (eGFR), and albuminuria significantly affects CKD staging through a dual classification system that considers both eGFR and albumin excretion, as recommended by Kidney Disease: Improving Global Outcomes (KDIGO) 1. The CKD stages are defined as follows:

• Stage 1 represents kidney damage with normal or increased eGFR (≥90 mL/min/1.73m²)
• Stage 2 indicates mild reduction in eGFR (60-89 mL/min/1.73m²)
• Stage 3 is divided into 3a (45-59 mL/min/1.73m²) and 3b (30-44 mL/min/1.73m²), representing moderate reduction
• Stage 4 shows severe reduction (15-29 mL/min/1.73m²)
• Stage 5 indicates kidney failure (<15 mL/min/1.73m² or dialysis) Albuminuria is categorized into three levels:
• A1 (normal to mildly increased, <30 mg/g)
• A2 (moderately increased, 30-300 mg/g)
• A3 (severely increased, >300 mg/g) The dual classification system, which considers both eGFR and albuminuria, creates a more comprehensive risk assessment matrix, where a patient with the same eGFR but higher albuminuria would be considered at greater risk for progression, as noted in the 2023 standards of care in diabetes 1. For example, someone with Stage 3a CKD and severe albuminuria (A3) faces higher risks than someone with the same eGFR but normal albuminuria (A1), highlighting the importance of considering albuminuria in CKD staging and management, as also supported by the 2024 standards of care in diabetes 1. The degree of albuminuria may influence the choice of antihypertensive or glucose-lowering medications, and observed history of eGFR loss and cause of kidney damage may also affect treatment decisions, as discussed in the context of CKD management 1.

From the Research

CKD Stages

• The different CKD stages are defined based on the estimated Glomerular Filtration Rate (GFR) and the degree of proteinuria (albuminuria) 2, 3, 4.
• The CKD-EPI equation is used to estimate GFR, and cystatin C level measurement can be considered if patients have factors that might make creatinine-based equations inaccurate 3, 4.
• CKD is classified into stages based on estimated GFR, degree of proteinuria, and the cause 3.

Albuminuria and CKD Staging

• Albuminuria is strongly associated with future risk for cardiovascular and kidney outcomes, and has been proposed to be included in the classification of CKD along with GFR 5.
• However, albuminuria is not associated with complications after controlling for GFR in patients younger than 70 years of age with non-diabetic CKD and GFR less than 90 ml/min/1.73 m2 5.
• The KDIGO guidelines define and stage acute and chronic kidney diseases by GFR and albuminuria, and recommend measuring serum creatinine and reporting estimated GFR based on serum creatinine (eGFRcr) using the CKD-EPI equation 4.

CKD Management

• Optimal management of CKD includes cardiovascular risk reduction, treatment of albuminuria, avoidance of potential nephrotoxins, and adjustments to drug dosing 2.
• Patients with CKD require monitoring for complications such as hyperkalemia, metabolic acidosis, hyperphosphatemia, vitamin D deficiency, secondary hyperparathyroidism, and anemia 2.
• Those at high risk of CKD progression should be promptly referred to a nephrologist 2.