Blood urea nitrogen, a substance in the blood, is an indicator of kidney function and is a product of protein metabolism. Clinically, the two indicators of blood urea nitrogen and creatinine are often applied to evaluate kidney function. The normal blood urea nitrogen value is between 2.5 and 7.5 mmol/l. If it exceeds 7.5, it is called elevated blood urea nitrogen, which in most cases indicates renal failure, that is, a decrease in the detoxification capacity of the kidneys. Renal failure can be acute renal failure caused by certain nephrotoxic drugs, or chronic renal failure caused by diabetic nephropathy, chronic glomerulonephritis, and these chronic diseases. Urea nitrogen is a product of protein metabolism, some patients with normal kidney function may also have mildly elevated urea nitrogen, consider and high protein diet has a lot to do with, such as eating more meat, milk or eggs, this situation does not require special treatment.