The causes of elevated blood urea nitrogen are divided into two types, one is exogenous causes, such as excessive protein food intake, and the other is due to renal disease, gastrointestinal bleeding, high fever and other causes. 1. Urea nitrogen is a product of protein metabolism, if the patient consumes too much protein food at one time, or constipation, etc., it can also cause transient elevation of blood urea nitrogen. 2. Another reason for elevated blood urea nitrogen is that the kidneys are damaged. When patients suffer from certain renal diseases, blood urea nitrogen can be seen to be elevated in the examination. For example, the patient suffers from nephritis disease, urinary tract infarction and so on. 3. Gastrointestinal bleeding will make the blood flow through the intestinal tract is absorbed, blood protein is broken down after the intestinal tract will absorb a large number of nitrogenous substances, which will indirectly cause the blood urea nitrogen rise. 4. Hyperthermia: patients with hyperthermia have an increased demand for energy and are prone to the phenomenon of negative nitrogen balance, which will consume protein function. This leads to an increase in the production of urea nitrogen and an increase in blood urea nitrogen. When the blood urea nitrogen is high, it is recommended to go to the hospital for examination, to clarify the cause of the disease, and to follow the doctor’s instructions for timely treatment.