BUN (Blood Urea Nitrogen) measures urea, a waste product made when the liver breaks down protein. The kidneys remove it. Some labs report 'urea' instead; urea in mg/dL is about 2.14 times the BUN.
- Normal range (adults)
- 7–20 mg/dL (2.5–7.1 mmol/L)
- Sample
- Blood
- Fasting
- Not usually needed
- Also called
- BUN, Blood Urea Nitrogen, Urea, Serum Urea, S.Urea, Blood Urea, Urea Nitrogen, Urea nitrogen
Blood Urea Nitrogen normal range
| Group | mg/dLConventional units: US, South Asia | mmol/LSI units: UK, Europe, Australia, international |
|---|---|---|
| Adults | 7–20 | 2.5–7.1 |
Your report may use either unit system; labs in the Gulf often print both. Ranges also vary slightly between laboratories, so the range printed on your own report is the one to go by.
Why is the Blood Urea Nitrogen test done?
It is part of the kidney function test, read together with creatinine.
What does a high Blood Urea Nitrogen level mean?
A high BUN may mean the kidneys are not filtering well, but it also rises with dehydration, a high-protein diet or bleeding in the stomach.
Common causes
- Dehydration
- Kidney disease
- High-protein diet
- Bleeding in the stomach or upper gut
- Heart failure
- Steroid medicines
Diet and lifestyle tips
- Drink enough water
- Avoid very high-protein diets and protein supplements
- Keep salt moderate
What does a low Blood Urea Nitrogen level mean?
A low BUN is usually not a concern.
Common causes
- Low-protein diet
- Liver disease
- Pregnancy
- Overhydration
Diet and lifestyle tips
- Eat adequate protein
When should you see a doctor?
See a doctor if BUN and creatinine are both high, or if you have black stools or vomiting blood.
Last updated
This page is for general education and is not a diagnosis. Normal ranges differ between laboratories, so always compare your result with the reference range printed on your own report, and discuss abnormal results with your doctor.