A BUN, or Blood Urea Nitrogen test, measures the level of urea nitrogen in the blood using a standard blood sample. Urea nitrogen is the natural byproduct of the breakdown of protein.
According to the American Association for Clinical Chemistry, BUN tests are mainly used to assess kidney health. However, altered BUN counts can be the result of almost any disease, drug, or condition that affects the kidneys or liver.
As such, the test may be requested as part of routine checkups. BUN tests are also included in common blood tests, such as metabolic panels.
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Why and when are BUN levels measured?
Medical professionals use BUN tests for a number of reasons, mostly to check or monitor kidney and liver function.
A BUN test uses a blood sample to check blood urea nitrogen levels.
As the waste product of protein digestion, the liver and kidneys influence blood urea nitrogen levels heavily.
Urea is released by the liver into the blood and sent to the kidneys to be removed in the urine. Nitrogen is found in urea and is also the compound responsible for helping clear excess nitrogen from the body. For this reason, "urea" and "urea nitrogen" are often used to mean the same thing.
A component of many other blood tests, BUN tests may be ordered for just about anyone at any time. They require only a blood sample. A BUN test may also be done alongside other kidney tests, such as the creatine test.
BUN tests are usually ordered in cases of suspected kidney or liver disease. Though common in adults, signs of these diseases are easily overlooked or mistaken for other conditions.
According to the Centers for Disease Control and Prevention (CDC), 10 percent of adults in the United States have long-term kidney disease. Many people are unaware that they have the condition.
Signs of kidney disease:
- Frequent urination, especially at night
- Change in urine volume
- A burning sensation during urination
- Foamy, coffee-, or blood-colored urine
- Joint or bone pain, especially in the area surrounding the kidneys
- Muscle cramps
- Restless legs during sleep
- Interrupted sleep
- Lack of concentration or alertness
- Poor appetite
- Swelling or puffiness, especially around the face, wrists, ankles, stomach, and thighs
- High blood pressure
Signs of liver disease:
- Dark colored urine
- Pale, bloody, or tar-colored stool
- Skin and eyes that appear yellow
- Bruising easily
- Loss of appetite
- Nausea or vomiting
- Weight loss
- Ongoing tiredness or weakness
- Stomach pain and swelling
- Swelling in the legs and ankles
Things to consider before taking a BUN test
The National Institute of Diabetes and Digestive and Kidney Diseases explain that a range of medications can impact BUN levels, or how the kidney and liver work. Over-the-counter painkillers, in particular NSAIDS or non-steroidal anti-inflammatory drugs, can all affect the kidneys. This class of drugs includes ibuprofen, naproxen, and aspirin.
Natural diuretics, such as caffeine, and steroid use can also affect the kidneys. Antibiotics can also impact BUN levels.
There are many prescription drugs that can affect the kidneys, resulting in abnormal BUN levels, including:
Many drugs such as penicillin can affect the kidneys and BUN levels.
- Amphotericin B
- Thiazide diuretics
According to the National Kidney Foundation, dietary supplements can also have a negative effect on the kidneys and alter BUN levels.
Generally, natural health products are not regulated by the U.S. Food and Drug Administration (FDA). This means that the effective dosage, source, and even the precise mixture of the supplement is questionable.
This lack of regulation also means herbal supplements may contain kidney-damaging compounds like heavy metals or chemicals like aristolochic acid.
People with kidney or liver disease are normally advised to avoid natural supplement. They are also advised to limit or monitor phosphorous and potassium intake.
Preparing for the BUN test
Preparing for a BUN test is relatively simple. Those undergoing the test are advised to eat and drink as normal before the test. This helps ensure that results are more of a reflection of long-term levels.
Bringing a list of current medications and supplements on the day of the test can be helpful.
To perform the BUN test, a medical professional will draw blood from a vein. They will often use a vein on the inside of the elbow or outside of the hand. Technicians will then examine the blood sample.
After the sample has been drawn and the proper waiting period has passed, most people immediately return to their usual routine. The results will be sent to the requesting physician.
If the puncture site becomes painful, inflamed, or weeps pus or blood, the patient should seek medical attention. After the test, some patients may also feel faint, hungry, or dehydrated.
Interpreting the results of a BUN test
A rise or fall in blood urea nitrogen levels may indicate a wide range of health problems. This is because the kidneys and liver are involved in a wide range of body functions.
According to the Medical Council of Canada, normal blood urea nitrogen levels range between 7 and 22 milligrams per deciliter. A result higher than 50 milligrams per deciliter is likely to signal an underlying health problem.
Elevated BUN levels can result from:
High BUN levels can be caused by kidney damage, failure, or disease.
- Kidney damage, failure, or disease
- Urinary tract blockages or disease
- Gut disease or bleeding
- Heart attack
- Heart failure
- Eating too much protein
- Intense stress
- Poor circulation
- High cholesterol
Low BUN counts can result from:
- Liver failure
- Not eating enough protein
- Poor nutrition
Changes in BUN levels also occur with age and gender, among individuals, and during pregnancy.
Typically, BUN levels increase with age. BUN counts in toddlers are just 66 percent of those in an average healthy adult, and rates in those over 60 are just higher than in young adults.
Typical BUN levels by age and gender:
- Children: 5 to 18 milligrams per deciliter
- Adult men: 8 to 20 milligrams per deciliter
- Adult women: 6 to 20 milligrams per deciliter
BUN tests can also help determine the effectiveness of kidney treatments like dialysis.
Follow-up treatments and tests
BUN tests alone are not enough to diagnose any condition.
If BUN results come back as abnormal, medical professionals will usually follow up with other tests. A creatinine test and renal panel can help indicate kidney and liver health. Testing may be done to determine specific substance levels as well, like potassium, sodium, and calcium. Urine tests may also be ordered.
In some instances, physicians may also follow up abnormal BUN results by requesting tests to evaluate the blood creatinine to BUN ratio. The ratio of BUN to creatinine is usually between 10:1 and 20:1.
The course of treatment for each person with abnormal BUN levels varies depending on the cause and severity of the case. Those with organ failure often need intensive treatment, and dialysis may be necessary. Lesser BUN problems may simply require long-term monitoring.
In the case of abnormal BUN levels brought about by eating too much protein, people can limit eating food rich in protein, like meat, fish, beans, and dairy, and increasing fruit and vegetable intake. Staying hydrated also helps prevent the buildup of BUN.
BUN levels have also been tied to high blood pressure and conditions that cause restricted blood flow such as diabetes. As stress can greatly impact blood pressure, exercising, seeking counseling, and reducing stress levels may help steady BUN levels. Controlling blood sugar levels can also promote healthy BUN levels.