BUN in medical terms refers to urea nitrogen, which is an item in kidney function, and its normal value is between 2.5 and 7.5 mmol/L. If it is lower than 2.5 mmol/L, it is called urea nitrogen reduction. If it is lower than 2.5 mmol/L, it is usually related to malnutrition or weight loss and strict dietary control, which is usually not harmful to the body. If the urea nitrogen is elevated and creatinine is normal, it may be related to a high protein diet, such as the high protein foods mentioned above.