Why blood urea nitrogen test done
You may need a BUN test: If your doctor suspects that you have kidney disease or damage. If your kidney function needs to be evaluated, especially if you have a chronic condition such as diabetes or high blood pressure.

Blood urea normal range:

The normal range of urea nitrogen in blood or serum is 5 to 20 mg/dl or 1.8 to 7.1 mmol urea per liter. The range is wide because of normal variations due to protein intake, endogenous protein catabolism, state of hydration, hepatic urea synthesis, and renal urea excretion."