Overview

A common blood test, the blood urea nitrogen (BUN) test reveals important information about how well your kidneys are working. A BUN test measures the amount of urea nitrogen that's in your blood.

Here's how your body typically forms and gets rid of urea nitrogen:

• Your liver produces ammonia — which contains nitrogen — after it breaks down proteins used by your body's cells.
• The nitrogen combines with other elements, such as carbon, hydrogen and oxygen, to form urea, which is a chemical waste product.
• The urea travels from your liver to your kidneys through your bloodstream.
• Healthy kidneys filter urea and remove other waste products from your blood.
• The filtered waste products leave your body through urine.

A BUN test can reveal whether your urea nitrogen levels are higher than normal, suggesting that your kidneys may not be working properly.