The blood urea nitrogen (BUN) test is a blood test that measures the level of urea nitrogen in the blood. Urea is a waste product produced by the liver as it breaks down proteins, and it is normally excreted by the kidneys in the urine. The BUN test is often used as a screening tool to assess kidney function, as an elevated BUN level can indicate decreased kidney function. Other conditions that can cause elevated BUN levels include dehydration, heart failure, liver disease, and high protein intake. A BUN test is usually ordered along with a creatinine test to get a more complete picture of kidney function. Treatment for high BUN levels depends on the underlying cause and may involve addressing any kidney or liver problems, rehydration, or dietary changes.