Renal failure is characterized by inability of the kidneys to clear metabolic waste products from the body and impaired fluid regulation, acid base regulation, hormonal functions (blood pressure regulation, stimulation of red blood cell production, calcium regulation and bone metabolism). Renal failure may be divided into acute and chronic forms. The causes may be prerenal (e.g. poor blood flow to the kidneys), renal (disease of the kidneys themselves, through diabetes or longterm high blood pressure) and postrenal (impaired flow of urine through the ureters). There are various causes for postrenal failure, e.g. stones or tumor within the ureter or scarring of the ureter from previous surgery or radiotherapy as well as impaired bladder emptying as seen with an enlarged prostate. Symptoms of chronic renal failure include lethargy and fatigue and brown discolouration of the skin through accumulation of metabolic waste products. Characteristically there is a gradual increase in blood pressure. The treatment is dependent upon the cause. Surgical intervention is generally indicated for postrenal failure. If renal function continues to deteriorate and cannot be treated this will result in terminal renal failure which requires dialysis in order to clear the blood of metabolic waste products or possibly renal transplantation.