One of the main functions of blood is to carry proteins to cells throughout the body.  The cells digest the protein and a waste substance called urea nitrogen is created.  The blood goes through the kidneys, which remove the urea nitrogen from the blood and pass it out of the body in urine.  One of the tests standardly ordered by doctors is the blood urea nitrogen test or BUN. This test measures the amount of BUN in the blood and is an indicator of how well the kidneys are able to remove the urea nitrogen from the body.

The urea nitrogen is measured in the number of milligrams (thousandths of a gram) of urea nitrogen per deciliter or per 1/10 of a liter of blood. For most people, if they have a BUN level of between 7 milligrams to 20 milligrams of urea nitrogen per deciliter of blood, their kidneys are believed to be working properly.

If a person’s BUN level is over 20 milligrams of urea nitrogen per deciliter of blood, this is an indication that something is interfering with the proper function of the kidneys. It could be a symptom of dehydration which can be more easily tested for and corrected, or it may be an indicator of more serious kidney problems.

It is also common for people with diabetes, heart problems and kidney stones to have higher BUN levels.

Sometimes people who consume a very high ratio of protein to other types of foods will have a higher BUN level.  A lower than normal BUN level is often an indicator of possible liver problems, but it may also indicate a too low protein intake or even malnutrition.

The BUN test is often accompanied by a creatinine test which is explained on its own page.