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Post-renal causes of kidney failure results not from events before the kidneys or at the kidney level but after a normally working kidney has finished its work. This is also known as obstructive kidney failure. It is often caused by something blocking the elimination of urine produced by normal functioning kidneys. It is the rarest cause of acute kidney failure accounting for about 10 per cent of all cases. This type of failure can be reversed, unless the obstruction stays long enough to cause damage to kidney tissue, usually from the pressure buildup. The obstruction to the flow of urine can be at the ureteric level (the paired tubes that connect the kidneys to the urinary bladder) or at the bladder level. Obstruction of one or both ureters can be caused by kidney stones, which is very uncommon in children. Also, cancer of the urinary tract or structures near the urinary tract may obstruct the outflow of urine. Obstruction at the bladder level can be caused by bladder stone, blood clots, cancer of the bladder, prostatic enlargement as well as certain neurologic disorders of the bladder impairing its ability to contract. In children, especially males, the commonest cause is failure of a valve to obliterate, called posterior urethral valves. Some people may not show any symptoms or may show only very subtle changes, at least in the early stages. These may include; � Decreased urine production � Body swelling � Confusion Lethargy � Nausea, Vomiting � Severe anaemia Seizures and coma may occur in very severe acute kidney failure due to high levels of toxic substances accumulated in the body impairing smooth brain function. Kidney failure is often detected from blood or urine tests. For those with no symptoms, they may be picked up during routine medical checkups or because they don't feel well and can't tell why. Blood levels of urea and creatinine are high in kidney failure of prerenal origin. Electrolytes in the blood, particularly potassium, may be abnormally high or low because of improper filtering. When the duration and kidney failure is severe, the red blood cell count may be low. This is from lack of erythropoietin, a hormone produced by the kidneys which helps in the production of red blood cells. The amount of urine produced over a period of hours may also be measured for quantity and quality or the amount of waste being excreted. When kidney tissue is injured, proteins and desirable substances may be inappropriately excreted in the urine. If the diagnosis is not certain after laboratory tests, an ultrasound of the kidneys and bladder may be done. These can help reveal signs of specific causes of kidney failure. In some cases, tissue samples of the kidneys are taken (biopsy) to find the cause of the renal failure. Use of nuclear medicine to diagnose is also effective in diagnosing kidney failure. Treatment of acute renal failure depends partly on the cause and extent of the failure. Care is usually administered by a nephrologist (kidney specialist). The first goal is to pinpoint the exact cause of the kidney failure, as that will partly dictate the treatment. Secondly, the degree to which accumulated wastes and water are affecting the body will impact treatment decisions about medications and the need for dialysis. Before dialysis though, treatment modalities include; � Correct dehydration � intravenous fluids, with electrolyte replacement if needed � Fluid restriction - For those types of kidney failure in which excess fluid is not appropriately eliminated by the kidneys � Increase blood flow to the kidney - Usually related to improving heart function or increasing blood pressure � Correct chemical (electrolyte) abnormalities - Keeps other body systems working properly. Relieving the obstructed path of urine flow improves the kidney function. In the absence of full recovery of kidney function, an artificial kidney is used to clear excess water and accumulating wastes. This is called dialysis, a process by which the blood is cleared of wastes and excess water. Dialysis is done by accessing the blood vessels through the skin (hemodialysis) or by accessing the abdominal cavity through the lining that encases the abdominal organs (peritoneal dialysis). As the blood passes through the dialysis machine, the toxins and waste products normally excreted by the kidneys are extracted from the blood which is returned to the body. Most people with acute kidney failure improve when the cause of the kidney failure is removed or treated and don't require dialysis. Normal kidney function is usually restored, though in some cases, residual damage only allows partial restoration of the kidney function. Such patients may not require dialysis but may need medicines to supplement lost kidney function. Those with chronic renal failure will need chronic dialysis or kidney transplant.