Blood Urea Nitrogen (BUN) is a medical test that measures the amount of urea nitrogen in the blood. Urea is a waste product formed when the body breaks down proteins. The kidneys filter urea from the blood, and its levels can indicate how well the kidneys are functioning. A high BUN level may suggest kidney problems, dehydration, or a high-protein diet, while a low level can indicate liver issues or malnutrition. Doctors often use BUN results alongside other tests, such as creatinine, to assess kidney health and overall metabolic function.