More recently also called acute kidney injury. Many times this is reversible but depending on the cause and severity, it may be irreversible and lead to chronic renal failure or chronic kidney disease. Normally, the kidneys filter the blood and remove waste and excess salt and water. Acute kidney failure is when the kidneys suddenly stop working. Acute renal failure can be due to many different causes. Generally these causes can be divided into three categories. Pre-renal means the cause is before the kidney or glomerulus. Generally, this is caused by a decrease in the amount of blood that gets to the kidney. Examples include heart failure, liver failure, shock. Another class of acute renal failure is post-renal. In this type, there is an obstruction to the flow of urine from the kidney. The most common example is prostate problems in men, urinary tract cancers, which directly obstruct the urine flow, or cancers in the abdomen or pelvis that push on the ureters that carry the urine from the kidney to the bladder. The last category is termed renal and is due to damage to the kidney itself, especially the filtering units (glomeruli) or the tubules leading from the glomeruli. Examples of renal injury include infections, cancer, some medications and other nephrotoxins, and auto-immune diseases. As well, primary kidney diseases (glomerulonephritis and nephrotic diseases, such as membranous nephropathy) can damage the kidneys and cause acute renal failure as well as chronic renal failure. Treatment generally is directed at support of blood pressure and flow of the blood to the kidneys. As well, any offending agents should be discontinued and any nephrotoxic agents should be avoided. Some cases will be severe enough to require dialysis to remove toxins from the body until the kidneys can recover. Sometimes, the damage is severe enough that it is irreversible and the patient will require long-term dialysis or renal transplant.