Blood Urea Nitrogen (BUN)

What is Blood Urea Nitrogen?

Blood Urea Nitrogen (BUN) measures the amount of nitrogen in your blood that comes from urea, a waste product formed when your liver breaks down proteins. Your kidneys filter urea from the blood, making BUN a marker of kidney function.

Why is it Tested?

Doctors order BUN to assess kidney function, monitor kidney disease progression, evaluate dehydration, and screen for various conditions affecting protein metabolism. It’s included in basic and comprehensive metabolic panels.

Normal Ranges

Reference ranges for BUN:

Normal: 7–20 mg/dL

Values may be slightly higher in elderly individuals and can vary with protein intake and hydration status.

Reference ranges vary by authority. Track yours across multiple standards with automatic unit conversions in LabsVault.

What do Abnormal Results Mean?

Abnormal results are not a diagnosis. Always discuss your results with a qualified healthcare provider before making any medical decisions.

Low BUN

Reduced levels may indicate:

Severe liver disease
Malnutrition or low protein diet
Overhydration
Pregnancy

High BUN

Elevated levels suggest:

Kidney disease or dysfunction
Dehydration
High protein diet
Heart failure
Gastrointestinal bleeding
Certain medications

How to Track Over Time

BUN levels help monitor kidney function over time, especially when evaluated alongside creatinine. Rising trends may indicate declining kidney function, while stable levels suggest adequate renal health. The BUN-to-creatinine ratio provides additional diagnostic information.

Blood Urea Nitrogen