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Blood Urea Nitrogen (BUN) Test
Find information on a blood urea nitrogen test. Learn how to prepare for the test, what to expect during the test, and how to interpret your te...

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What Is a BUN Test?

The kidneys are two bean-shaped organs located on each side of the spine. They’re responsible for filtering out of the blood waste products, excess water, and other impurities. These important organs also control the pH, salt levels, and potassium levels in the body. The kidneys even produce hormones that manage red blood cell production and regulate blood pressure.

A blood urea nitrogen (BUN) test is used to determine how well your kidneys are working. It does this by measuring the amount of urea nitrogen in the blood. Urea nitrogen is a waste product that’s created in the liver when the body breaks down proteins. Normally, the kidneys filter out this waste, and urinating removes it from the body.

BUN levels tend to increase when the kidneys or liver are damaged. Having too much urea nitrogen in the blood or having high BUN levels can be a sign of kidney or liver problems.

Why Is a BUN Test Done?

This fast, simple blood test is most commonly used to evaluate kidney function. It’s often done along with other tests to make a proper diagnosis. For example, your doctor may order a blood creatinine test. This test measures the amount of creatinine in your blood. Creatinine is another chemical waste product that your kidneys normally filter out of the blood. When the kidneys aren’t working correctly, creatinine can build up in your body.

The BUN test can help diagnosis the following conditions:

The test may even be used to determine the effectiveness of dialysis treatment.

How Do I Prepare for a BUN Test?

The BUN test doesn’t require any special preparation. However, it’s important to tell your doctor if you’re taking any prescription or over-the-counter medications. Certain medications can affect your BUN levels.

Some medications, including chloramphenicol or streptomycin, may lower your BUN levels. Other drugs, such as antibiotics and diuretics, may increase your BUN levels.

Commonly prescribed medicines that may raise your BUN levels include:

  • amphotericin B
  • carbamazepine
  • cephalosporins
  • furosemide
  • methotrexate
  • methyldopa
  • rifampin
  • spironolactone
  • tetracycline
  • thiazide diuretics
  • vancomycin

Be sure to tell your doctor if you’re taking any of these medications. Your doctor will take this information into consideration when reviewing your test results.

How Is a BUN Test Performed?

This simple test involves taking a small sample of blood.

Before drawing blood, a technician will clean an area of your upper arm with an antiseptic. They’ll tie an elastic band around your arm, which will make your veins swell with blood. The technician will then insert a sterile needle into the vein and draw blood into a tube attached to the needle. You may feel slight to moderate pain when the needle goes in.

Once they collect enough blood, the technician will remove the needle and apply a bandage over the puncture site. They’ll send your blood sample to a laboratory for testing. Your doctor will follow up with you to discuss the test results.

What Do the Results of a BUN Test Mean?

Results of the BUN test are measured in milligrams per deciliter (mg/dL). Normal BUN values tend to vary depending on gender and age. It’s also important to note that each laboratory has different ranges for what’s normal.

In general, normal BUN levels fall in the following ranges:

  • adult men: 8 to 20 mg/dL
  • adult women: 6 to 20 mg/dL
  • children: 5 to 18 mg/dL

Higher BUN levels can indicate:

  • congestive heart failure or recent heart attack
  • gastrointestinal bleeding
  • high protein levels
  • kidney disease
  • kidney failure
  • dehydration
  • obstruction in the urinary tract
  • shock

Lower BUN levels can indicate:

  • liver failure
  • malnutrition
  • severe lack of protein in the diet

Depending on your test results, your doctor may also run other tests to confirm a diagnosis or recommend treatments.

What Are the Risks of a BUN test?

Unless you’re seeking care for an emergency medical condition, you can typically return to your normal activities after taking a BUN test. Tell your doctor if you have a bleeding disorder or you’re taking certain medications such as blood thinners. This may cause you to bleed more than expected during the test.

Side effects associated with the BUN test include:

  • bleeding at the puncture site
  • bruising at the puncture site
  • feeling faint
  • accumulation of blood under the skin
  • infection at the puncture site

Notify your doctor if you experience any unexpected or prolonged side effects after the test.

Written by: Rachel Nall
Edited by:
Medically Reviewed by:
Published: Jul 25, 2012
Published By: Healthline Networks, Inc.
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