Figure 1. The 5-stage model for kidney disease progression according to National Kidney Foundation Kidney Disease Outcomes Quality Initiative classification of chronic kidney disease. Stage 1 (glomerular filtration rate, or GFR, ≥ 90 mL/min/1.73 m²) indicates kidney damage with normal or increased GFR, stage 2 (GFR, 60-89 mL/min/1.73 m²) indicates kidney damage with mildly decreased GFR, stage 3 (GFR, 30-59) indicates moderate kidney disease, stage 4 (GFR, 15-29) indicates severe kidney disease, and stage 5 (GFR, < 15 mL/min/1.73 m²) indicates kidney failure or dialysis.