Why it's done

You may need a BUN test:

• If your doctor suspects that you have kidney disease or damage
• If your kidney function needs to be evaluated, especially if you have a chronic condition such as diabetes or high blood pressure
• To help determine the effectiveness of dialysis treatment if you're receiving hemodialysis or peritoneal dialysis
• As part of a blood test group to help diagnose a number of other conditions, such as liver damage, urinary tract obstruction, congestive heart failure or gastrointestinal bleeding — although an abnormal BUN test result alone doesn't confirm any of these conditions

If kidney problems are the main concern, the creatinine levels in your blood will likely also be measured when your blood is tested for urea nitrogen levels. Creatinine is another waste product that healthy kidneys filter out of your body through urine. High levels of creatinine in your blood may be a sign of kidney damage.

Your doctor may also test how well your kidneys are removing waste from the blood. To do this, you may have a blood sample taken to calculate your estimated glomerular filtration rate (GFR). The GFR estimates the percentage of kidney function you have.