What is a BUN test?

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 can be a sign of kidney or liver problems.

Why is a BUN test done?

A BUN test is a blood test most commonly used to evaluate kidney function. It’s often done along with other blood tests, such as a creatinine blood test, to make a proper diagnosis.

A BUN test can help diagnose the following conditions:

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

BUN tests are also often performed as part of regular checkups, during hospital stays, or during or after treatment for conditions like diabetes.

While a BUN test measures the amount of urea nitrogen in the blood, it doesn’t identify the cause of a higher or lower than average urea nitrogen count.

How do I prepare for a BUN test?

A 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 certain antibiotics and diuretics, may increase your BUN levels.

Commonly prescribed medications that may raise your BUN levels include:

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

How is a BUN test performed?

A BUN test is a simple test that 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 a vein and draw blood into a tube attached to the needle. You may feel mild 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 a 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, fall in the following ranges:

  • adult men: 8 to 24 mg/dL
  • adult women: 6 to 21 mg/dL
  • children 1 to 17 years old: 7 to 20 mg/dL

Normal BUN levels for adults over 60 are slightly higher than normal levels for adults under 60.

Higher BUN levels can indicate:

Keep in mind that some medications, such as certain antibiotics, can raise your BUN levels.

Lower BUN levels can indicate:

Depending on your test results, your doctor may also run other tests to confirm a diagnosis or recommend treatments. Proper hydration is the most effective way to lower BUN levels. A low-protein diet can also help lower BUN levels. A medication wouldn’t be recommended to lower BUN levels.

However, abnormal BUN levels don’t necessarily mean you have a kidney condition. Certain factors, such as dehydration, pregnancy, high or low protein intake, steroids, and aging can impact your levels without indicating a health risk.

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 a BUN test include:

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

In rare cases, people become lightheaded or faint after having blood drawn. Notify your doctor if you experience any unexpected or prolonged side effects after the test.

The takeaway

A BUN test is a quick and simple blood test commonly used to evaluate kidney function. Abnormally high or low BUN levels don’t necessarily mean you have problems with kidney function. If your doctor suspects you have a kidney disorder or another health condition, they will order additional tests to confirm a diagnosis and determine the cause.