Whether urea nitrogen 7.9 mmol/L is serious should be determined by the cause of the elevated urea nitrogen. Physiologic causes are usually not serious, while pathologic causes are relatively serious. The normal level of urea nitrogen in normal adults is 3.2-7.1mmol/L. Urea nitrogen 7.9mmol/L is higher than the upper limit of normal value. 1. Physiological fluctuation: because urea nitrogen is the product of protein metabolism in the body, through glomerular filtration and then excreted with urine, so when a large amount of protein intake, the body protein catabolism increases, so the level of urea nitrogen will be elevated, drink more water to promote its excretion, and stop a large amount of intake of protein can be restored to normal on its own. 2. Pathological diseases: gastrointestinal bleeding, renal insufficiency and other diseases can also be elevated urea nitrogen levels. (1) Gastrointestinal bleeding: Whether it is upper gastrointestinal bleeding or lower gastrointestinal bleeding, blood remains in the gastrointestinal tract, and red blood cells are mainly composed of proteins, so red blood cells are decomposed and metabolized in the gastrointestinal tract and the level of urea nitrogen will increase, and at the same time there may be fatigue, palpitations and other symptoms, which need to be consulted immediately, and the gastrointestinal endoscopy and other examinations can help to make a clear diagnosis. (2) Renal insufficiency: When renal insufficiency occurs, the glomerular filtration rate decreases, and the excretion of urea nitrogen decreases, which will lead to elevated blood urea nitrogen level, and may be accompanied by nausea, fatigue and other symptoms, and it is recommended to consult the doctor in time, and the tests such as blood creatinine test and ultrasound of the urinary tract can assist in making a clear diagnosis. When the urea nitrogen level is found to be elevated, it is recommended to consult a doctor in time, after clarifying the cause of the disease, and then follow the doctor’s instructions to give targeted treatment.