If the urine volume is less than 400ml in 24 hours, it is considered pathological oliguria, which needs to be treated in hospital. 1. It may be caused by the kidney itself, such as acute renal failure, glomerulonephritis, nephrotic syndrome, etc., because the abnormal function of the kidney itself leads to reduced filtration, which results in oliguria, and all water is accumulated in the patient’s body, so the patient will appear swollen face and limbs. 2. It may also be due to prerenal factors, such as dehydration, nausea, vomiting without timely hydration, or sweating more without hydration, so that the blood volume filtered through the kidneys is reduced, and oliguria will occur. 3. It may also be due to postrenal causes, such as the presence of stones leading to obstruction of the urinary tract, and the urine produced by the kidneys It cannot be discharged into the bladder, it will not be discharged out of the body, or in men with prostate hyperplasia, all the urine accumulates within the bladder and the urethra is obstructed and cannot be discharged out of the body, which also causes oliguria. These need to be examined at the hospital to clarify before dealing with them.