The blood urea nitrogen (BUN) test is used along with serum creatinine test to evaluate the renal status, to diagnose renal disease, and to monitor the treatment. Urea is a waste product of protein metabolism, produced in the liver. urea is released into the blood and carried to the kidneys, where it is filtered and released into the urine. Since this is a continuous process, there is usually a minute amount of urea in the blood. However, the levels of blood urea increase when there is renal disease or damage. When the creatinine and BUN tests results are abnormal or if a person has diseases such as diabetes or hypertension, these tests may be used to monitor the renal status and effectiveness of treatment. Blood creatinine and BUN tests may also be done to know the status of renal prior to procedures, such as a CT scan which may require the use of nephrotoxic drugs and dyes. Normally the levels of BUN may vary, but usually, high blood urea nitrogen (BUN) levels are a sign of improper functioning of kidneys. High BUN levels can also be due to dehydration, burns, high protein diet and use of certain medications, etc.