Urea nitrogen is a product of protein catabolism in the body. Urea nitrogen is often used clinically to reflect renal function, and the presence of elevated urea nitrogen often indicates renal insufficiency. Low urea nitrogen has no particular clinical significance. Because urea nitrogen is a product of protein metabolism, it is closely related to diet. Low protein intake can lead to low urea nitrogen, as well as physiological low urea nitrogen in women during pregnancy. In addition, patients with malnutrition can also have low urea nitrogen, and finally, low urea nitrogen is often seen in patients with liver failure. Because the liver is the site of protein synthesis in the body, liver failure can lead to reduced protein synthesis and abnormal protein consumption.