Blood urea nitrogen

Blood urea nitrogen (BUN) measures the amount of nitrogen in your blood that comes from urea, a waste product created when your liver breaks down proteins. Your kidneys filter urea from your blood and remove it in urine, so BUN levels provide important information about both kidney function and protein metabolism. Elevated levels may indicate that your kidneys aren't filtering waste effectively, or could reflect dehydration, high protein intake, or increased protein breakdown in the body. Low levels are less common but can occur with severe liver disease or malnutrition.