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BUN - blood test

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 typically 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 medications without talking to your doctor 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.

Normal Results

The normal result is generally 6 - 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:

Lower-than-normal levels may be due to:

  • Liver failure
  • Low protein diet
  • Malnutrition
  • Over-hydration

Considerations

For people with liver disease, the BUN level may be low even if the kidneys are normal.

Alternative Names

Blood urea nitrogen

References

Landry DW, Basari H. Approach to the patient with kidney disease. In: Goldman L, Schafer AI, eds. Cecil Medicine. 24th ed. Philadelphia, Pa: Saunders Elsevier; 2011:chap 116.

Update Date: 4/29/2013

Updated by: David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine. Also reviewed by A.D.A.M. Health Solutions, Ebix, Inc., Editorial Team: David Zieve, MD, MHA, Bethanne Black, Stephanie Slon, and Nissi Wang.

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