Blood urea nitrogen (BUN) | Healthmatters.io (2024)

What Is Blood Urea Nitrogen (BUN)?

Urea nitrogen is a waste product. It develops when your body breaks down the protein in the foods you eat. It forms in your liver and travels through your blood to your kidneys, which then filter it out of your blood. It leaves your body through your urine. When your kidneys are healthy, they remove the BUN, usually leaving a small amount of it in the blood. But for the most part, your kidneys get rid of it by flushing it out of your body through urine. When your kidneys are not working well, your BUN level goes up. Over time, this may lead to serious health problems, including high blood pressure, anemia, and heart disease.

Your blood urea nitrogen (BUN) level is based on a blood test that measures the amount of urea nitrogen in your blood.

- BUN is a waste product of cell metabolism. You get protein from the food you eat, and it enters the bloodstream from the intestines to be used by cells throughout your body.

- Your cells break protein down into amino acids to build back up into the proteins they need for various processes. This produces nitrogen-containing ammonia as a byproduct, which is excreted into the bloodstream.

- The liver transforms ammonia into urea to make it less toxic and sends the urea out into the bloodstream. Urea is filtered out of the blood by the kidneys.

- If all is going well, there is a continuous amount of urea being produced and being excreted by the kidneys into the urine. The BUN level in the blood is, therefore, stable. If the kidneys are damaged and not functioning properly, urea and the nitrogen it contains are not filtered fully from the blood.

The blood urea nitrogen (BUN) test measures how much urea nitrogen is in your blood. It helps a healthcare provider determine if your kidneys are working as they should.

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

What are normal BUN levels?

BUN levels vary according to your age and sex. Abnormal levels may indicate a health condition, including kidney damage.

Normal Ranges in mg/dL by ages:

0-2 years: 4-15
3-16 years: 9-18
17-64 years: 8-22
>64 years: 10-28

What is the purpose of the BUN test?

Urea nitrogen levels in your blood are one marker that allows healthcare providers to understand how well your kidneys are working. A small amount of urea nitrogen in your blood is normal. If you have too much urea nitrogen in your blood, your kidneys aren’t filtering it properly. You may have a condition that’s affecting your kidneys’ health.

The biomarker Blood urea nitrogen (BUN) is part of a standardized blood test panel called the Comprehensive Metabolic panel (CMP). This panel is usually performed at your biannual health check up.

Your health care professional might also perform this test if you:

a) have symptoms of kidney disease, such as urinary changes, swelling in your arms or legs, muscle cramps, or frequent episodes of fatigue, or

b) if you have a higher risk of kidney disease because of diabetes, cardiovascular problems, or a family history of kidney disease.

c) need to monitor for side effects when you begin a new medication that can affect the kidneys.

Your doctor may also test how well your kidneys are removing waste from the blood. To do this, you may have a blood sample taken to calculate your estimated glomerular filtration rate (GFR). The GFR estimates the percentage of kidney function you have.

You may need a BUN test for other reasons. Depending on your overall health, it may be part of a routine health check to find out how your kidneys are working. If you need dialysis or medicine for kidney function, you may have the test to check the health of your kidneys before the procedure, after the procedure, or both. BUN tests are also routine during hospital stays for certain conditions.

You may be more likely to develop kidney disease if you have:

- Family of kidney problems

- Diabetes

- High blood pressure

- Heart disease

What are symptoms of later stage kidney disease?

Your provider may check your BUN levels if you are having symptoms of later stage kidney disease, such as:

- Needing to urinate more often or less often than usual

- Itching

- Fatigue

- Swelling in your legs, feet, or ankles

- Muscle cramps

- Trouble sleeping

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:

- Creatinine, which is another waste product that your kidneys remove from your body

- GFR (Glomerular Filtration Rate), which estimates how well your kidneys are filtering blood

What might affect my test results?

Your BUN levels might rise even if your kidneys are working as they should for many reasons. These include:

- A high-protein diet

- Steroid use

- Dehydration

- Burn injuries

- Aging

This is why the ratio of BUN levels to creatinine levels is a more reliable measure of kidney health.

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FAQs:

Is Blood urea nitrogen (BUN) the same as urea?

Blood Urea Nitrogen (BUN) and urea are related but not exactly the same. Here’s the distinction?

Urea:

- Urea is a chemical compound with the formula (NH2)2CO.

- It is a waste product formed in the liver through the urea cycle, which converts ammonia, a byproduct of protein metabolism, into urea.

- Urea is then transported to the kidneys via the bloodstream, where it is excreted in urine.

Blood Urea Nitrogen (BUN):

- BUN is a measurement of the nitrogen portion of urea in the blood.

- The BUN test is used to evaluate kidney function. Higher levels of BUN indicate that the kidneys may not be filtering urea properly.

- The term 'nitrogen' in BUN refers specifically to the nitrogen atom that is part of the urea molecule.

In summary, BUN is a specific measure of the nitrogen content in urea found in the blood, while urea itself is the actual compound that contains nitrogen.

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