Kidney failure or End-Stage Renal Disease (ESRD) is defined as a state when the kidneys do not function properly or sufficiently, resulting in the accumulation of waste products and toxic materials.
When toxic wastes build in the blood, they may cause permanent and irreversible damage to body cells, tissues and organs. Thus, in order to survive, kidney function needs to be replaced either through dialysis or transplant.
A person can stay healthy with just one kidney. Individuals with kidneys that function below 20% of their required capacity, however, need some form of renal replacement therapy.