BUN stands for blood urea nitrogen. Urea nitrogen is what forms when protein breaks down.
A test can be done to measure the amount of urea nitrogen in the blood.
How the Test is Performed
A blood sample is needed. Most of the time blood is drawn from a vein located on the inside of the elbow or the back of the hand.
How to Prepare for the Test
Many medicines can interfere with blood test results.
- Your health care provider will tell you if you need to stop taking any medicines before you have this test.
- DO NOT stop or change your medicines without talking to your provider first.
How the Test will Feel
You may feel slight pain or a sting when the needle is inserted. You may also feel some throbbing at the site after the blood is drawn.
Why the Test is Performed
The BUN test is often done to check kidney function.
The normal result is generally 6 to 20 mg/dL.
Note: Normal values may vary among different labs. Talk to your doctor about your specific test results.
The examples above show the common measurements for results for these tests. Some laboratories use different measurements or may test different specimens.
What Abnormal Results Mean
Higher-than-normal levels may be due to:
- Congestive heart failure
- Excessive protein levels in the gastrointestinal tract
- Gastrointestinal bleeding
- Hypovolemia (dehydration)
- Heart attack
- Kidney disease, including glomerulonephritis, pyelonephritis, and acute tubular necrosis
- Kidney failure
- Urinary tract obstruction
Lower-than-normal levels may be due to:
- Liver failure
- Low protein diet
For people with liver disease, the BUN level may be low even if the kidneys are normal.
Blood urea nitrogen
Landry DW, Basari H. Approach to the patient with renal disease In: Goldman L, Schafer AI, eds. Goldman-Cecil Medicine. 25th ed. Philadelphia, PA: Elsevier Saunders; 2016:chap 114.
Review Date 4/30/2015
Updated by: Laura J. Martin, MD, MPH, ABIM Board Certified in Internal Medicine and Hospice and Palliative Medicine, Atlanta, GA. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.