Renal replacement therapy (RRT) is therapy that replaces the normal blood-filtering function of the kidneys. It is used when the kidneys are not working well, which is called  renal failure and includes acute kidney injury and chronic kidney disease. Renal replacement therapy includes dialysis (hemodialysis or peritoneal dialysis), hemofiltration, and hemodiafiltration, which are various ways of diverting the blood into a machine, cleaning it, and then returning it to the body. Renal replacement therapy also includes kidney transplantation, which is the ultimate form of replacement in that the old kidney is replaced by a donor kidney.