1. Causes of renal underperfusion secondary to: (1) decreased cardiac output; (2) blood loss; (3) hypotension; (4) dehydration syndrome; (5) postoperative period; (6) late oncological disease; (7) ADH secretion syndrome; (8) use of vasoconstrictive drugs. Common causes of pre-renal renal failure include vomiting, diarrhea, dehydration, hemorrhage, burns, etc. It can also be seen in conditions such as severe edema and ascites (relative blood volume deficiency). 2.Pathogenesis Although there is no organic lesion of the kidney in all the above causes, the production of non-protein nitrogen is not reduced, but the excretion of non-protein nitrogen through the kidney is affected, resulting in azotemia and hypochlorhydria. 3. Pre-signs (1) generalized swelling: almost all of them have different degrees of swelling, and the swelling is most obvious in the face, lower limbs and scrotum. The swelling may last for weeks or months, or it may subside at times throughout the course of the disease. After infection (especially streptococcal infection), the swelling often recurs or worsens, and azotemia may even occur. (2) Gastrointestinal symptoms: Due to edema of the gastrointestinal tract, there are often symptoms of gastrointestinal dysfunction such as not thinking about eating and drinking, nausea, vomiting and abdominal distention. These symptoms are aggravated when azotemia is present. (3) Hypertension: an important clinical manifestation of non-nephrotic syndrome, but with water and sodium retention and increased blood volume, transient hypertension may occur. Type II primary nephrotic syndrome may be accompanied by hypertension. (4) Proteinuria: A large amount of proteinuria is the most important condition for the diagnosis of this syndrome. (5) Hypoproteinemia: mainly a decrease in plasma protein, the degree of which is significantly related to the degree of proteinuria. (6) Hyperlipidemia: Significant increase of triglycerides in the blood. (7) High urine foam that does not disappear for a long time: this indicates more protein excreted in the urine and discoloration of the urine. When the urine is thick tea-colored, wash water-like, soy sauce-colored or cloudy, such as rice water, seek immediate medical attention. Too much or too little urine. The average volume of urine in a normal person is 1500 ml per day, 4-8 times per day. If there is no fever, a lot of sweating, a lot of water, etc., and there is a sudden decrease or steep increase in the volume of urine, it is necessary to go to the hospital for examination to see if it is a kidney lesion. Nocturia. Normal people within 60 years of age should not normally have nocturia. If nocturia increases in young people, it is likely to be an early sign of poor kidney function. Edema. Edema on the eyelids or face after waking up in the morning, which mostly subsides in the afternoon, worsens after exertion and reduces after rest. Severe edema will appear on the inner side of both ankles, both lower limbs, and the lumbosacral region. Low back pain. Low back pain without a clear cause should be examined for kidney, crestal spine and muscles of the low back.