Blood Urea Nitrogen (BUN)

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  • Also Known As:
  • BUN
  • Urea Nitrogen
  • BUN to Creatinine Ratio
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Test Quick Guide

A blood urea nitrogen (BUN) test measures the amount of urea in a sample of blood. Urea is a waste product that forms as part of the body’s natural process of breaking down proteins. It is also referred to as urea nitrogen and is filtered out of the blood by the kidneys.

A BUN test is most often interpreted together with creatinine to help assess how well the kidneys are working. While BUN can be tested independently, it is normally included in a panel with other measurements, which offers a more extensive evaluation of the condition of your body.

About the Test

Purpose of the test

A blood urea nitrogen test can provide insight into how well the kidneys are working. The test may be used for diagnosis, screening, and/or monitoring. For these uses, BUN alone is generally less informative than BUN taken with other measurements related to kidney function.

Diagnosis is the term that describes the process of finding the cause when symptoms have already developed. BUN may be measured if you have symptoms of kidney disease such as urinary changes, swelling in your arms or legs, muscle cramps, or frequent episodes of fatigue.

Screening is trying to detect a health concern before signs or symptoms have appeared. A BUN test as part of a basic metabolic panel (BMP) or comprehensive metabolic panel (CMP) may be prescribed during regular medical check-ups to screen for potential kidney conditions. Screening may be prescribed for people who have a higher risk of kidney disease because of diabetes, cardiovascular problems, or a family history of kidney disease.

Monitoring is a way for a physician to track how a patient’s condition changes. Measuring blood urea nitrogen may be part of observing kidney function over time. A BUN test can provide relevant information for evaluating response to treatment for kidney problems.

Tests of kidney function, including a measurement of blood urea nitrogen, may also be used to monitor for side effects when you begin a new medication that can affect the kidneys.

What does the test measure?

As the test name indicates, a BUN test measures urea nitrogen in the blood. Urea, often called urea nitrogen, is a waste product that is produced as a result of the breakdown of proteins in the body.

The kidneys work to filter urea out of the blood so that it can be cleared out of the body in the urine. As this process unfolds, it’s normal for some urea to be in the blood. But when BUN levels are too high, it can be an indication that the kidneys are not functioning properly.

Although BUN can be tested individually, it is more common for it to be measured along with other substances in the blood that can reflect the functioning of the kidneys.

When should I get a blood urea nitrogen test?

Blood urea nitrogen is most commonly measured as part of the basic or comprehensive metabolic panel. These tests involve 8 and 14 measurements respectively and provide insight into multiple bodily systems, including kidney function.

A panel of tests with a BUN measurement included may be appropriate if you have symptoms of kidney disease. In addition, a test panel with BUN may be used to help with diagnosis when you have general symptoms or are being evaluated in an emergency room or urgent care.

Your physician may recommend screening tests including a BUN measurement if you have risk factors for kidney disease such as a family history of kidney problems, diabetes, or cardiovascular issues like high blood pressure.

Your doctor may also prescribe screening tests with a BUN measurement during routine medical exams. Though this type of testing is commonly done, there is no clear research showing that the benefits of routine screening are greater than its downsides, including the costs of testing and potential for unnecessary follow-up procedures.

If you have previously had an abnormal BUN test or have a known kidney problem, repeat testing at regular intervals may be appropriate in order to monitor your situation and current kidney function.

Finding a Blood Urea Nitrogen Test

How to get tested

Testing for blood urea nitrogen is normally prescribed by a doctor, and the test is performed using a sample of blood that is drawn from a vein in your arm. The blood draw normally takes place in a medical setting like a doctor’s office or laboratory.

While BUN can be tested alone, in most cases it is part of a panel of tests that includes multiple measurements from the same blood sample. For example, BUN is a standard component of the basic metabolic panel and comprehensive metabolic panel.

Can I take the test at home?

At-home tests are available that include a measurement of blood urea nitrogen. These tests do not typically measure BUN alone but rather involve a few additional measurements that are related to kidney function. For an at-home BUN test, you prepare a blood sample from the finger and send it by mail to a lab.

At-home tests that measure BUN are available without a prescription, but it is still recommended that you talk with your doctor before and after taking an at-home test. If you have an abnormal result, your doctor may want to repeat the test or conduct more comprehensive testing using a blood sample taken from a vein.

How much does the test cost?

Blood urea nitrogen testing does not have a set cost. Instead, the cost depends on where you have the test taken and whether you have health insurance coverage. The cost will also vary based on whether BUN is tested alone or in a panel with other measurements.

The total cost of a BUN test includes several different components including charges for an office visit, a blood draw by a technician, and laboratory analysis. These costs are often covered by health insurance if the test has been prescribed for you by your doctor.

Check with your insurance company and your doctor’s office for more detailed information about test costs, and make sure to ask whether you will be responsible for a deductible or copay.

At-home tests that include BUN in a panel of measurements related to kidney health are available for around $100, which usually includes the costs for shipping your sample.

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Taking a Blood Urea Nitrogen Test

This test measures urea nitrogen in the blood, so testing requires a blood sample. This sample is taken from a vein in your arm with a needle.

If BUN is being measured as part of an at-home test, the sample is a drop of blood taken from your finger.

Before the test

When scheduling your test, you should tell your doctor about any prescription drugs, over-the-counter medications, and/or dietary supplements that you usually take. Some of these can affect a BUN test, so your doctor may ask you to modify your medication schedule before the test.

Other types of preparations, including fasting, are not normally needed for a test of BUN alone. However, if BUN is being tested with other measurements such as in a basic or comprehensive metabolic panel, you will likely be instructed to fast for 8-12 hours before the blood draw.

For an at-home test, you should ask your doctor or check with the included instructions for details about any required preparations, including any changes to your medications.

During the test

After being seated, a technician will tie an elastic band around the top part of your arm in order to increase blood flow in your veins. They will use an antiseptic to disinfect the area of your arm where the blood will be drawn, which is typically on the inside part of your elbow.

The technician will insert a sterile needle into your vein and use it to remove a small vial of blood. After that, the needle will be removed, and the collection is finished.

Overall, the test usually takes just a few minutes during which you may feel some temporary pain or a stinging sensation.

For an at-home test, you’ll use an included device with a very small needle to prick your fingertip. You then put a drop of blood on a test strip that is then mailed to a laboratory.

After the test

Applying pressure to the puncture site with a bandage or cotton swab can prevent bleeding after your blood has been drawn. You may notice some bruising or tenderness in your arm, but if this occurs, it tends to go away quickly.

You can usually return to your normal activities, including working and driving, after the test. Consider bringing a snack for after the test if you were instructed to fast beforehand.

It is uncommon to have any ongoing side effects after an at-home BUN test, but if your fingertip continues to bleed, you can apply pressure with a small bandage.

Blood Urea Nitrogen (BUN) Test Results

Receiving test results

After your blood draw, you will typically get the results within a few business days. It is common to get a copy of the test report by mail or have access to it online through a health care portal. Your doctor’s office may also call or send you a secure electronic message to provide information about your results.

Because an at-home test kit has to be sent by mail to the lab, it is normal for it to take a couple of additional days to receive your test results. In most cases, the results are available online or through a smartphone app.

Interpreting test results

The test report should include a line for blood urea nitrogen that shows the level found in your sample as well as the laboratory’s reference range. BUN is measured in milligrams per deciliter of blood (mg/dL).

Working with your doctor is the best way to understand the significance of your BUN test. The American Board of Internal Medicine lists a typical reference range for blood urea nitrogen as 8 to 20 mg/dL. However, this range is not universal. Labs can use different methods to measure BUN, and what constitutes a normal result can vary from lab to lab.

If you had a panel test, you should see separate test results for any other measurements taken along with blood urea nitrogen. Each test component will have the listed reference range for the laboratory that conducted your test.

Your doctor can discuss your BUN levels and how they relate to your overall health, any symptoms you have, and other test measurements. This is important because BUN levels alone are not a consistent predictor of kidney function. Elevated BUN can occur with kidney problems, but it can also happen from eating lots of protein, taking certain medications, or from other issues like dehydration or burns. BUN levels often rise with aging as well.

Independently, blood urea nitrogen may not reflect kidney function. For this reason, it is often interpreted in the context of other measurements, such as creatinine, a breakdown product of the muscle, that is filtered by the kidneys. In some cases, the doctor may look at the ratio of BUN to creatinine to help determine the underlying cause of the altered kidney function.

Abnormally low levels of BUN can be a sign of malnutrition, lack of protein in the diet, and liver disease. Therefore, other tests included in a panel test like the comprehensive metabolic panel may provide helpful information for understanding the significance of low blood urea nitrogen.

Are test results accurate?

Laboratory methods for measuring BUN are considered to be reliable for medical interpretation and use. While no medical test is perfect, protocols exist to reduce errors in drawing your blood, preparing your sample, and analyzing it in the lab.

Do I need follow-up tests?

If you have an abnormal result on your BUN test, you may need follow-up testing. This could include an expanded panel of measurements along with BUN if this kind of testing was not conducted initially. Tests to further evaluate kidney function, such as the estimated glomerular filtration rate (eGFR), may be performed.

Depending on the interpretation of the test results, other laboratory tests or imaging tests may be needed to definitively diagnose any underlying condition that is affecting your health.

Questions for your doctor about test results

Some questions that may be helpful when you go over your blood urea nitrogen test results with your doctor include:

  • Was my BUN level normal or abnormal?
  • Were any other measurements taken along with BUN?
  • What do the test results mean for my kidney function?
  • If my test was abnormal, what is the most likely explanation for that result?
  • Should I repeat the BUN test at any point or have any other follow-up tests?

Related Content

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Elsewhere on the Web

View Sources

A.D.A.M. Medical Encyclopedia. Comprehensive metabolic panel. Updated January 26, 2019. Accessed May 13, 2021. https://medlineplus.gov/ency/article/003468.htm

A.D.A.M. Medical Encyclopedia. Basic metabolic panel. Updated April 29, 2019. Accessed May 13, 2021. https://medlineplus.gov/ency/article/003462.htm

A.D.A.M. Medical Encyclopedia. BUN – blood test. Updated April 29, 2019. Accessed May 13, 2021. https://medlineplus.gov/ency/article/003474.htm

American Board of Internal Medicine. ABIM laboratory test reference ranges. Updated January 2021. Accessed May 13, 2021. https://www.abim.org/Media/bfijryql/laboratory-reference-ranges.pdf

Gounden V, Bhatt H, Jialal I. Renal function tests. In: StatPearls. Updated July 20, 2020. Accessed May 19, 2021. https://www.ncbi.nlm.nih.gov/books/NBK507821/

Hosten AO. Chapter 193: BUN and Creatinine. In: Walker HK, Hall WD, Hurst JW, eds. Clinical Methods: The History, Physical, and Laboratory Examinations. 3rd edition. 1990. Accessed May 19, 2021. https://www.ncbi.nlm.nih.gov/books/NBK305/

Inker LA, Perrone RD. Lab interpretation: high blood urea nitrogen in adults. In: Sterns RH, ed. UpToDate. Updated June 26, 2019. Accessed May 18, 2021. https://www.uptodate.com/contents/high-blood-urea-nitrogen-in-adults

Inker LA, Perrone RD. Assessment of kidney function. In: Sterns RH, ed. UpToDate. Updated April 29, 2021. Accessed May 19, 2021. https://www.uptodate.com/contents/assessment-of-kidney-function

MedlinePlus: National Library of Medicine. BUN (blood urea nitrogen). Updated July 30, 2020. Accessed May 13, 2021. https://medlineplus.gov/lab-tests/bun-blood-urea-nitrogen/

MedlinePlus: National Library of Medicine. Comprehensive metabolic panel (CMP). Updated March 2, 2021. Accessed May 13, 2021. https://medlineplus.gov/lab-tests/comprehensive-metabolic-panel-cmp/

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