What is the normal range for Blood Urea Nitrogen (BUN)?

• A. 10-22 mg/dL
• B. 5-10 mg/dL
• C. 23-40 mg/dL
• D. 0-5 mg/dL

Answer: (A)

BUN reflects how well the kidneys are clearing nitrogenous waste produced by protein metabolism in the liver. In healthy adults, this value typically sits in the low to mid teens up to the low twenties, and a common reference range used in exams is about 10 to 22 mg/dL. This range accounts for normal variations due to hydration and protein intake. Values above this range can indicate reduced kidney function, dehydration, high protein intake, or catabolic states, while values well below it can occur with overhydration, liver disease, or very low protein intake. The other options fall outside the usual normal window, so they’re not considered normal.