Have you heard of the blood urea nitrogen (BUN) test? It is a standard blood test that helps determine how well your kidneys are working. Learn more about it here, including what urea nitrogen is, why a BUN test is ordered, and what abnormal results can mean. 

How is BUN related to your kidneys? 

BUN is a test that measures the urea nitrogen in your blood. To understand why urea nitrogen is related to the kidneys, you need to know that: 

• Your liver produces a chemical called ammonia, which contains nitrogen after it breaks down protein in your body.
• A waste product called urea is produced from that nitrogen in combination with other elements such as carbon, hydrogen, and oxygen.
• The urea travels from your liver to your kidneys, where it is filtered and waste products are removed. 

When your kidneys are not working at full capacity, urea nitrogen can build up and cause you to have higher BUN levels. 

When is a BUN test needed?

A BUN test may be ordered by your doctor for a number of reasons, including: 

• If kidney disease or damage is suspected
• If your kidney function needs to be evaluated because of other health conditions such as diabetes or high blood pressure
• To help determine if your dialysis treatments are effective 
• As part of a group of blood tests to help diagnose or rule out other health conditions, such as liver damage, urinary tract obstruction, or congestive heart failure

How to prepare and what to expect 

When blood samples are being tested specifically for BUN, you are allowed to eat and drink normally prior to the test. In cases where multiple tests are being done, you may need to fast for a certain amount of time before the blood work. 

During the test, a healthcare worker will take a sample of your blood by inserting a needle into a vein in your arm. The sample is then sent to a lab for analysis, and you are able to return to your usual daily activities. 

What do the results mean? 

While normal BUN ranges may vary depending on your age and the particular lab, generally, the 6 to 24 mg/dL range is considered normal.

An elevated BUN can mean that your kidneys are not working properly, but it can also suggest: 

• Dehydration (from insufficient fluid intake or other reasons)
• Urinary tract obstruction
• Congestive heart failure or recent heart attack
• Gastrointestinal bleeding
• Shock
• Severe burns
• Certain medications, including some antibiotics
• A high-protein diet

Oftentimes BUN levels increase with age, and infants are expected to have lower levels. Your doctor can explain your results and discuss BUN and other blood work metrics further with you.  

*Blood urea nitrogen (BUN) test – Mayo Clinic. (2021, August 19). https://www.mayoclinic.org/tests-procedures/blood-urea-nitrogen/about/pac-20384821