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Blood Urea Nitrogen

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Also known as: BUN; Urea Nitrogen; Urea
Formal name: Blood Urea Nitrogen

The Test Sample

What is being tested?

Urea is a waste product formed in the liver when protein is metabolized into its component parts (amino acids) . This process produces ammonia, which is then converted into the less toxic waste product urea. This test measures the amount of urea nitrogen in the blood.

Nitrogen is a component of both ammonia and urea. Urea and urea nitrogen are referred to somewhat interchangeably because urea contains nitrogen and because urea/urea nitrogen is the "transport method" used by the body to rid itself of excess nitrogen. Urea is released by the liver into the blood and is carried to the kidneys, where it is filtered out of the blood and released into the urine. Since this is an ongoing process, there is usually a small but stable amount of urea nitrogen in the blood.

Most diseases or conditions that affect the kidneys or liver have the potential to affect the amount of urea present in the blood. If increased amounts of urea are produced by the liver or if the kidneys are not working properly and have difficulty filtering wastes out of the blood, then urea concentrations will rise in the blood. If significant liver damage or disease inhibits the production of urea, then BUN concentrations may fall.

How is the sample collected for testing?

A blood sample is drawn from a vein in the arm.

NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.

Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.

Is any test preparation needed to ensure the quality of the sample?

No test preparation is needed.