blood urea nitrogen

Definition of blood urea nitrogen
National Cancer Institute

blood urea nitrogen

(blud yoo-REE-uh NY-troh-jen)
Nitrogen in the blood that comes from urea (a substance formed by the breakdown of protein in the liver). The kidneys filter urea out of the blood and into the urine. A high level of urea nitrogen in the blood may be a sign of a kidney problem. Also called BUN and urea nitrogen.

Source: NCI Dictionary of Cancer Terms