Chronic Kidney Disease Definitions and Classifications

Introduction to CKD Stages

The National Kidney Foundation defines a non-functional kidney as having a GFR <15 mL/min per 1.73 m², which is accompanied in most cases by signs and symptoms of uremia, and is also defined by the need to start kidney replacement therapy (dialysis or transplantation) 1, 2, 3
The Kidney Disease: Improving Global Outcomes (KDIGO) classification system defines Stage 5 CKD (G5) as a GFR <15 mL/min per 1.73 m², which corresponds to kidney failure and loss of approximately 90% or more of normal kidney function 1, 4, 5, 6

The American College of Physicians recommends that CKD be classified into five stages based on GFR, with Stage 3a (G3a) defined as GFR 45-59 mL/min per 1.73 m², and Stage 3b (G3b) defined as GFR 30-44 mL/min per 1.73 m² 4, 5, 6
The National Institute of Diabetes and Digestive and Kidney Diseases states that a GFR <60 mL/min per 1.73 m² represents loss of half or more of normal adult kidney function, and below this threshold, the prevalence of CKD complications increases substantially 1, 2, 3

The Kidney Disease: Improving Global Outcomes (KDIGO) guideline recommends that GFR be estimated using validated equations (MDRD Study equation or CKD-EPI) based on calibrated serum creatinine, and that factors affecting eGFR accuracy include extremes of muscle mass, non-steady state conditions, and advanced age 4
The American Society of Nephrology notes that decreased GFR in the elderly remains an independent predictor of adverse outcomes including death and cardiovascular disease, and that the definition of CKD is the same regardless of age 1, 2, 3