Clinically, a 24-hour urine output of less than 400 ml is called oliguria, and a 24-hour urine output of less than 100 ml is called anuria. The causes of oliguria and anuria can be divided into three main categories: 1. Pre-renal: such as heart failure, shock, severe hypoproteinemia, liver disease, severe dehydration, etc. It is mainly caused by insufficient renal perfusion and decreased glomerular filtration. 2, renal: the most common, such as acute nephritis, acute tubular necrosis, uremia, acute renal failure, lupus nephritis, etc. It is mainly due to impaired filtration of the glomerulus and or tubular necrosis and swelling blockage, resulting in the inability to produce urine . 3.Postrenal: such as bilateral kidney stones, bladder stones, bladder tumors, idiopathic retroperitoneal hyperplasia, etc. Strictly speaking certain posterior renal causes cannot yet be described as oliguria or anuria. For example, blockage of the urethra caused by bladder stones, which prevents urination, is not that the kidneys do not produce urine, but that urine is retained in the bladder and cannot be expelled, mistakenly because the kidneys do not produce urine. A blockage that lasts too long can likewise cause the kidneys to be injured and not produce urine. The longer the duration of oliguria and anuria lasts the worse the prognosis, and it can even cause irreversible damage.