Generally speaking, the amount of urine output is determined by the amount of water drunk and the excretory function of the body. Drink more water, sweat more, urinate more. If the water you drink is not proportional to the urine you excrete, or if you can’t drink and excrete, there is a problem with the water filtration and excretion function of the human kidneys. So, how much urine per day or per hour is considered to be less urine? Generally, according to the human body’s activity, the normal 24-hour urine volume should not be <400 ml, or the average hourly urine volume is less than 17 ml, otherwise it will be edema. Does anuria mean no urine at all? Anuria is not the absence of urine or the absence of drops of urine. Anuria is defined as a total urine output of <100 ml in 24 hours or nothing in 12 hours. There are many factors that can cause anuria, such as hepatorenal syndrome, renal vein embolism, acute glomerular necrosis, obstruction of the renal pelvis and ureter caused by various reasons, obstruction or abnormal function of the bladder neck caused by kidney stones, prostate disease, and acute renal failure caused by retroperitoneal fibrosis and tumor compression of neighboring organs, resulting in oliguria or anuria. This oliguria and anuria that cannot be corrected within a short period of time may lead to acute renal failure, which is life-threatening and should be immediately treated by a doctor.