What is the commonly accepted reference range for blood urea nitrogen (BUN) in mg/dL?

• A. 6-20 mg/dL
• B. 10-40 mg/dL
• C. 2-8 mg/dL
• D. 30-60 mg/dL

Answer: (A)

Blood urea nitrogen reflects how well the kidneys are clearing urea, a waste product from protein breakdown, from the blood. The commonly accepted normal range for adults is about 6 to 20 mg/dL. This range is used because it fits typical kidney function, hydration status, and protein intake in healthy individuals, though exact cutoffs can vary slightly by lab method and patient factors.

Values within this window are considered normal because the kidneys are effectively filtering urea. Higher values can indicate dehydration, reduced kidney function, high protein intake, or other stressors that raise urea production or reduce clearance. Lower values can occur with very low protein intake or significant liver disease where urea production is diminished. Among the given options, the range around six to twenty milligrams per deciliter best matches the standard reference range.