Medical Health Encyclopedia

BUN

How the test will feel:

When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.

Why the test is performed:

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The BUN test is a somewhat routine test used primarily to evaluate renal (kidney) function. The test is often performed on patients with many different diseases.

Urea is formed in the liver as the end product of protein metabolism. During digestion, protein is broken down to amino acids. Amino acids contain nitrogen, which is removed as NH4+ (ammonium ion), while the rest of the molecule is used to produce energy or other substances needed by the cell. The ammonia is combined with other small molecules to produce urea. The urea makes its way into the blood and it is ultimately eliminated in the urine by the kidneys.

Most renal diseases affect urea excretion so that BUN levels increase in the blood. Patients with dehydration or bleeding into the stomach and/or intestines may also have abnormal BUN levels. Numerous drugs also affect BUN by competing with it for elimination by the kidneys.

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