Normal blood urea nitrogen, or BUN, level ranges from 6 to 20 milligrams per deciliter of blood, according to MedlinePlus. This range may vary from one laboratory to another because laboratories may differ in terms of specimens tested and measurements used.
Blood urea nitrogen forms from the breakdown of proteins, notes MedlinePlus. Doctors determine the level of BUN through a blood test. The test helps determine how well the kidneys are working. The BUN that is higher than normal may indicate conditions such as congestive heart failure, kidney failure, kidney disease and congestive heart failure. If the BUN is lower than the normal range, conditions such as liver failure, malnutrition and low protein diet are the possible causes.