Urea nitrogen is a nitrogenous compound in blood plasma other than protein, which is excreted from the body by glomerular filtration. Urea nitrogen is mainly excreted by the kidneys and can reflect the glomerular filtration rate, so when urea nitrogen is elevated, it often represents impaired kidney function. Urea nitrogen is an indicator used to assess kidney function, and is often seen together with creatinine. When kidney function is impaired, and urea nitrogen is predominantly elevated, this is often indicative of pre-renal renal insufficiency, which is commonly caused by diarrhea, profuse sweating and ischemia of the kidneys due to cardiac insufficiency. If the urea nitrogen and creatinine are elevated simultaneously, then it suggests parenchymal kidney injury. The most common causes are glomerulonephritis, chronic renal insufficiency, etc. If the urea nitrogen is low, this condition is common in people who are malnourished with protein or have a small body size and low muscle capacity, generally speaking there is no big problem, pay attention to more meat, eggs, milk and other protein foods. Therefore, urea nitrogen is a very important indicator in the blood biochemistry to assess the kidney function, its increase and decrease, as well as the magnitude of the increase, can reflect the condition of our body to a certain extent.