The BUN (Blood Urea Nitrogen) test measures the amount of urea nitrogen in your blood. Urea nitrogen is a waste product formed when your body breaks down protein. Your liver produces ammonia from protein metabolism, which then combines with other elements to form urea. This urea travels through the bloodstream to your kidneys, which filter it out and remove it from your body through urine

. The BUN test is primarily used to assess how well your kidneys are functioning. Healthy kidneys filter urea effectively, keeping BUN levels within a normal range, typically about 7 to 20 mg/dL, though this can vary slightly by lab

. Elevated BUN levels may indicate kidney problems, such as kidney disease or damage, or other conditions like dehydration, heart failure, or gastrointestinal bleeding. Low BUN levels can be seen in liver disease, malnutrition, or overhydration

. In summary, the BUN test is a key indicator of kidney health and helps detect kidney dysfunction early, often alongside other tests such as creatinine and eGFR