Results of the blood urea nitrogen test are measured in milligrams per deciliter (mg/dL) in the United States and in millimoles per liter (mmol/L) internationally. In general, 7 to 20 mg/dL (2.5 to 7.1 mmol/L) is considered normal. But normal ranges may vary, depending on the reference range used by the lab, and your age. Ask your doctor to explain your results.
Urea nitrogen levels tend to increase with age. Infants have lower levels than other people do, and the range in children varies.
Generally, a high blood urea nitrogen level means your kidneys aren't working well. But elevated urea nitrogen can also be due to:
- Urinary tract obstruction
- Congestive heart failure or recent heart attack
- Gastrointestinal bleeding
- Dehydration, resulting from not drinking enough fluids or for other reasons
- Severe burns
- Certain medications, such as corticosteroids and some antibiotics
- A high protein diet
If kidney damage is a concern, ask your doctor what factors may be contributing to the damage and what steps you can take to try to control them.
Jul. 03, 2013
- The kidneys and how they work. National Kidney and Urologic Diseases Information Clearinghouse. http://kidney.niddk.nih.gov/kudiseases/pubs/yourkidneys/. Accessed May 30, 2013.
- BUN. Lab Tests Online. http://labtestsonline.org/understanding/analytes/bun/tab/test. Accessed June 8, 2013.
- Taal MW, et al. Brenner & Rector's The Kidney. 9th ed. Philadelphia, Pa.: Saunders Elsevier; 2011. http://www.mdconsult.com/books/about.do?about=true&eid=4-u1.0-B978-1-4160-6193-9..C2010-1-67932-1--TOP&isbn=978-1-4160-6193-9&uniqId=321553651-265. Accessed May 30, 2013.
- Inkler LA, et al. Assessment of kidney function. http://www.uptodate.com/home. Accessed May 30, 2013.
- Anderson CF (expert opinion). Mayo Clinic, Rochester, Minn. June 11, 2013.
- Castle EP (expert opinion). Mayo Clinic, Rochester, Minn. June 19, 2013.
- National Kidney Foundation. Tests to measure kidney function, damage and detect abnormalities. http://www.kidney.org/atoz/content/kidneytests.cfm. Accessed June 25, 2013.