What is a BUN (Blood Urea Nitrogen) Test?

A BUN, or blood urea nitrogen test, measures the amount of urea nitrogen in your blood. Urea nitrogen is a waste product that forms as your body breaks down proteins. It's carried in your blood and then removed by your kidneys when you urinate (pee).

Having a small amount of urea nitrogen in your blood is normal. But higher-than-normal BUN levels may be a sign that your kidneys aren't working well. If you have kidney disease, this waste material can build up in your blood and may lead to serious health problems, including high blood pressure, anemia, and heart disease.

People with early kidney disease may not have any symptoms. A BUN test can help uncover kidney problems early, when treatment can be more effective.

Other names for a BUN test: Urea nitrogen test, serum BUN, BUN to Creatinine Ratio

What is it used for?

A BUN test is often part of a series of tests called a comprehensive metabolic panel (CMP). It can help diagnose or monitor kidney diseases.

Why do I need a BUN test?

Your health care provider may order a BUN test:

• As part of a routine checkup
• To monitor the treatment of a kidney disease
• For screening if you are at risk of a kidney problem, since early kidney disease usually does not have any signs or symptoms. You may be at risk of developing a kidney problem because of:
  • A family history of kidney problems
  • Diabetes
  • High blood pressure
  • Heart disease
  • Obesity
  • Being over the age of 60
  • Smoking or using other tobacco products

Your provider may also check your BUN levels if you are having symptoms of later-stage kidney disease, which can include:

• Needing to go the bathroom (urinate) frequently or infrequently
• Itching
• Fatigue
• Swelling in your arms, legs, or feet
• Muscle cramps
• Trouble sleeping

What happens during a BUN test?

A health care professional will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out. This usually takes less than five minutes.

Will I need to do anything to prepare for the test?

Usually, no special preparation is necessary for a BUN test. But if your provider has ordered other tests on your blood sample, you may need to fast (not eat or drink) for several hours before the test. Your provider will let you know if there are any special instructions.

Are there any risks to the test?

There is very little risk to having a blood test. You may experience slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.

What do the results mean?

Normal BUN levels can vary, but generally, a high blood urea nitrogen level is a sign that your kidneys are not working well. But abnormal results don't always mean that you have a medical condition that needs treatment. BUN levels can vary according to your sex. They also usually increase with age.

A few other reasons your BUN level might be higher than normal include:

• Dehydration (too little fluid in your body)
• Burns
• Certain medicines
• A high-protein diet
• A recent heart attack

A few other reasons your BUN levels might be lower than normal include:

• A lack of protein in your diet
• Malnutrition
• Liver disease

To learn what your results mean, talk to your provider.

Learn more about laboratory tests, reference ranges, and understanding results.

Is there anything else I need to know about a BUN test?

A BUN test is only one type of measurement of kidney function. If your provider thinks you may have kidney disease, you may need other tests. These may include tests to measure your:

• Creatinine, which is another waste product that your kidneys remove from your body
• GFR (Glomerular Filtration Rate), which gives an estimate of how well your kidneys are filtering blood