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. High levels of BUN may suggest kidney problems, dehydration, or a high-protein diet, while low levels can indicate liver issues or malnutrition. Doctors often use BUN results alongside other tests, such as creatinine, to assess overall kidney health and guide treatment decisions.