Urea nitrogen is a normal waste product that your body creates after you eat. Your liver breaks down the proteins in your food -- and while it does that, it creates blood urea nitrogen, also known as BUN. Your liver releases the substance into the blood, and it eventually ends up in your kidneys.
When your kidneys are not healthy, they have trouble removing BUN and leave more of it in your blood.
The blood urea nitrogen test, which is also called a BUN or serum BUN test, measures how much of the waste product you have in your blood. If your levels are off the normal range, this could mean that either your kidneys or your liver may not be working properly.
Why You Get the BUN Test
Your doctor may order a BUN test as part of a routine checkup. It may be one of several blood tests that you get.
If you have a kidney condition, the test is a way to check what your BUN levels are before you start a medication or treatment. Also, it’s standard for a BUN test to be given when you’re in the hospital for certain conditions.
If your doctor suspects you may be getting kidney problems, they may order the BUN test.
Tell your doctor if you have the following symptoms, which can be signs that something is wrong with your kidneys:
● A change in how much you urinate
● Pee that is foamy, bloody, discolored, or brown
● Pain while you pee
● Joint or bone pain
● Pain in the mid-back where kidneys are located
● You’re tired all the time
How Do I Prepare for the Test?
Before the blood test, tell your doctor what medications you’re taking. If any of them might alter the test result, your doctor may ask you to stop taking them for a period of time.
If you’re only getting a BUN test, you can eat and drink. But if you’re getting other blood tests, your doctor may give you directions that may include fasting before the test.
What Happens During the Test?
It may feel a little bit sore afterward, but you can go straight back to your everyday activities.
Your doctor’s office will send the blood sample to a lab to be analyzed. You should get the results in a few days, depending on how fast the lab and your doctor’s office can work.
Understanding Your Results
Your result will be a number that measures how much BUN is in your blood. The range considered normal is between 7 to 20 milligrams per deciliter. (A milligram is a very tiny amount -- more than 28,000 to an ounce, and a deciliter is equal to about 3.4 ounces).
If your test results are not in that range, talk to your doctor.
Several things can affect your BUN test results, so having a BUN level that is lower or higher than the normal range doesn’t always mean there is a problem.
Things that affect your BUN level might include:
● High-protein diet (may cause high BUN levels)
● Low-protein diet (may cause low BUN levels)
What High BUN Levels Can Mean
High BUN levels can also indicate various problems with your kidneys. Talk to your doctor about what could be causing the problem and plan your next steps.
High levels can also indicate the following:
● Urinary tract obstruction (blockage from being able to pee)
● Burn injuries
Low BUN levels are rare. If you have low BUN levels, it could indicate:
● Liver disease
● Malnutrition (when your diet doesn’t have enough nutrients or your body can’t take them in well)
● Overhydration (having too much fluid)
But a BUN test is not a way to diagnose these issues, so more tests may be needed
Your doctor may also order a creatinine test, which is another blood test that also checks your kidney health. This is because the BUN level by itself doesn’t always reveal much.
When your BUN levels are compared with your creatinine levels, it gives a fuller picture of what’s happening with your kidneys. This is known as the BUN/Creatinine ratio.
Creatinine is a waste product from your muscles that is also filtered by your kidneys. Like BUN, high levels of creatinine could mean there is a lot of waste product that hasn’t been removed by the kidneys.
The ideal ratio of BUN to creatinine falls between 10-to-1 and 20-to-1.
Having a ratio above this range could mean you may not be getting enough blood flow to your kidneys, and could have conditions such as congestive heart failure, dehydration, or gastrointestinal bleeding.
A ratio below the normal range could mean liver disease or malnutrition.