What is BUN?
Blood urea nitrogen (BUN) measures the nitrogen in urea, a waste product the liver makes from protein breakdown and the kidneys clear. BUN reflects kidney function but is also influenced by hydration, protein intake, and blood flow, so it is interpreted alongside creatinine and the BUN:creatinine ratio.
Why it matters
BUN helps assess kidney function and hydration. The BUN:creatinine ratio helps distinguish dehydration or bleeding from intrinsic kidney disease.
What it measures
The concentration of urea nitrogen in the blood, interpreted with creatinine.
Reference & optimal ranges
Reference ranges vary by lab, assay, age, and sex. The ranges below reflect commonly published adult intervals and are for education only always interpret results with the range printed on your own lab report and a clinician.
High BUN can indicate reduced kidney function, dehydration, high protein intake, or GI bleeding.
Common symptoms
- Often none
- Fatigue, confusion, or reduced urination if from advanced kidney disease
Potential causes
- Dehydration
- Kidney disease
- High-protein diet
- Heart failure (reduced kidney blood flow)
- GI bleeding
- Certain medications
Low BUN is uncommon and usually not concerning; it can reflect low protein intake, overhydration, or liver disease.
Common symptoms
- None typically
Potential causes
- Low-protein diet
- Overhydration
- Severe liver disease
- Pregnancy
How to improve your BUN
Lifestyle
Stay hydrated
Dehydration is one of the most common reasons for a mildly elevated BUN.
Nutrition
Balanced protein intake
Very high protein intake raises BUN; balance is best unless a clinician advises otherwise.
Exercise
Hydrate around activity
Adequate fluids around exercise support normal kidney values.
Sleep
General health
Supports cardiovascular health tied to kidney perfusion.
Frequently asked questions
Scientific references
- BUN (Blood Urea Nitrogen) Test MedlinePlus, U.S. National Library of Medicine
- BUN Test Testing.com
Educational information, not medical advice. This page is for general education and does not replace diagnosis or treatment by a licensed clinician. Do not start, stop, or change any medication, supplement, or treatment based on this content. Reference and optimal ranges vary between laboratories interpret your results with the range on your own report and a qualified professional.