What Does BUN (Blood Urea Nitrogen) Mean?
BUN measures nitrogen waste from protein breakdown. Elevated BUN can indicate dehydration, high protein intake, or kidney issues — best interpreted alongside creatinine.
What BUN (Blood Urea Nitrogen) Measures
When you digest protein, your liver produces urea as a waste product, and your kidneys filter it out. BUN measures the nitrogen portion of that urea in blood. The BUN/creatinine ratio helps doctors distinguish dehydration (high ratio) from true kidney problems (proportional rises).
Normal Ranges
Normal7–20 mg/dL
Mildly elevated20–30 mg/dL
Significantly elevated> 30 mg/dL
BUN/creatinine ratio normal10:1 to 20:1
Reference ranges may vary slightly by lab. Always use the range provided on your specific test report.
What Affects Your BUN (Blood Urea Nitrogen) Level
- Dehydration (most common cause of mild elevation)
- High-protein diet or protein supplements
- GI bleeding (digested blood acts like a high-protein load)
- Kidney impairment
- Heart failure (reduced kidney perfusion)
- Medications: steroids, tetracyclines
- Aging (gradual rise is normal)