Stage 1 : Reduced Renal Reserve, characterized by a 40% to 75% loss of nephron function. The patient usually does not have symptoms because the remaining nephrons are able to carry out the normal functions of the kidney.

Stage 2 : Renal Insufficiency occurs when 75% tp 90% of nephron functionis lost. At this point, the serum creatinine and blood urea nitrogen rise, the kidney loses its ability to concentrate urine and anemia develops.

Stage 3 : End-stage Renal Disease, the final stage of chronic renal failure occurs when there is less than 10% nephron fuction ramaining.

Note: Nephron is the functional unit of the kidney