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Definition
By Mayo Clinic staffA blood urea nitrogen (BUN) test reveals important information about how well your kidneys and liver are working.
A blood urea nitrogen test measures the amount of urea nitrogen — urea is a chemical waste product — that's in your blood. Your liver produces ammonia after it breaks down proteins used by your body's cells. The nitrogen from ammonia combines with other particles, such as carbon, hydrogen, and oxygen, to form urea. The urea travels from your liver to your kidneys through your bloodstream. Healthy kidneys filter urea and other waste products from your blood. The filtered waste products leave your body in urine.
If a blood urea nitrogen test reveals that your urea levels are higher than normal, it probably indicates that your kidneys aren't working properly. Or, it could point to high protein intake, inadequate fluid intake or poor circulation.
If a blood urea nitrogen test shows lower than normal levels, it could indicate liver disease or damage, or malnutrition. But a low BUN level wouldn't likely be the first indication of liver disease because the blood urea nitrogen test isn't used as a screening test for that disorder.
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- Your kidneys and how they work. National Kidney and Urologic Diseases Information Clearinghouse. http://kidney.niddk.nih.gov. Accessed Oct. 22, 2008.
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- 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.
