The main causes of elevated blood urea nitrogen levels include kidney failure, gastrointestinal bleeding, dehydration, urinary tract problems, heart disease and heart failure, states Healthline. The normal blood urea nitrogen levels range between 7 and 20 milligrams per deciliter, with variations from this requiring further testing to check kidney function.
The blood urea nitrogen or BUN test checks the amount of urea nitrogen in the blood to help diagnose or monitor kidney diseases and their treatments, explains Healthline. Urea nitrogen is a waste product that forms when protein breaks down in the body. In healthy patients, the kidneys usually filter the waste product, which then passes out through the urine. When the kidneys are unable to filter the urea nitrogen from the blood, the BUN level rises. Doctors usually recommend the BUN test to patients who are showing signs of kidney disorders. These signs include frequent urination, discolored urine, restless legs, swelling in the extremities and fatigue.
Levels of blood urea nitrogen that are higher or lower than normal do not always indicate a kidney disorder, cautions Healthline. Factors such as pregnancy, dehydration, aging, steroids, and high or low protein intake affect BUN test results even when the patient is healthy and is not suffering from any kidney disorders.