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Results
By Mayo Clinic staffResults 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. The normal range for blood urea nitrogen is generally 7 to 20 mg/dL (2.5 to 7.1 mmol/L). However, urea nitrogen levels vary by age. Infants have lower levels than other people do. Also, men have slightly higher levels than women do.
Generally, a high blood urea nitrogen level means your kidneys aren't working well, particularly if the result is above 50 mg/dL (17.8 mmol/L). But, elevated urea nitrogen can also be due to urinary tract obstruction, congestive heart failure or gastrointestinal bleeding. Your blood urea nitrogen level may also increase as a result of dehydration, shock, burns or fever. Certain medications, such as corticosteroids, may increase urea nitrogen levels, too. In addition, a high protein diet can cause your BUN level to increase.
Lower than normal blood urea nitrogen levels may be a sign of liver damage. But low levels can also be caused by malnutrition, a low-protein diet or a high-carbohydrate diet.
If the results of your BUN test are higher or lower than normal, your doctor may want to confirm the results with another blood or urine test.
If kidney damage is a concern, it's important to control any conditions that may be contributing to the damage. It's especially important to manage your blood pressure, which often requires medication. You can't undo permanent kidney damage, but with appropriate treatment you may be able to prevent further damage.
- Blood urea nitrogen. In: Nicoll D, et al. Pocket Guide to Diagnostic Tests. 5th ed. New York, N.Y.: McGraw-Hill Companies; 2008. http://www.accessmedicine.com/popup.aspx?aID=3135548&searchStr=blood urea nitrogen. Accessed Oct. 21, 2008.
- Your kidneys and how they work. National Kidney and Urologic Diseases Information Clearinghouse. http://kidney.niddk.nih.gov. Accessed Oct. 22, 2008.
- Lab Tests Online: BUN. American Association for Clinical Chemistry. http://labtestsonline.org/understanding/analytes/bun/test.html. Accessed Oct. 22, 2008
- Stevens L, et al. Assessment of kidney function: Serum creatinine; BUN; and GFR. http://www.uptodate.com/home/index.html. Accessed Oct. 22, 2008.
- Palevsky PM. Dialysis modality and dosing strategy in acute renal failure. Seminars in Dialysis. 2006;19:165.
- Nally JV. Acute renal failure in hospitalized patients. Cleveland Clinic Journal of Medicine. 2002;69:569.
- Morgan GE, et al. Anesthesia for patients with renal disease. In: Morgan GE, et al. Clinical Anesthesiology. 4th ed. New York, N.Y.: McGraw-Hill Companies; 2006. http://www.accessmedicine.com/content.aspx?aID=892940. Accessed Oct. 21, 2008.
- Reference values. Blood urea nitrogen. Rochester, Minn.: Mayo Foundation for Medical Education and Research; 2008.
