What is the normal BUN level range?

• A. 6-18 mg/dL
• B. 4-12 mg/dL
• C. 6-20 mg/dL
• D. 8-22 mg/dL

Answer: (C)

BUN reflects nitrogen from urea in the blood, a waste product formed in the liver and cleared by the kidneys. The normal range for BUN in adults is about 6–20 mg/dL. This interval is commonly used across many labs, though some reference ranges may start slightly higher or end at 22 mg/dL. So the value that fits the typical normal range is 6–20 mg/dL.

Interpreting BUN involves context. A higher BUN can signal dehydration, kidney dysfunction, high protein intake, GI bleeding, or increased protein breakdown. A lower BUN can occur with liver disease, malnutrition, or overhydration. Often BUN is considered alongside creatinine to assess kidney function, and the BUN/creatinine ratio can help distinguish prerenal from intrinsic kidney causes.