Test Quick Guide

A blood urea nitrogen (BUN) test measures the amount of urea in a blood sample. 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 often interpreted together with creatinine to help assess how well the kidneys work. 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 BUN 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 when taken with other measurements related to kidney function.

Diagnosis is the term that describes the process of finding the cause when signs and 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 checkups to screen for potential kidney conditions. Screening may be prescribed if you 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 your condition changes. Measuring BUN may be part of observing kidney function over time. A BUN test can provide relevant information for evaluating responses to treatment for kidney problems.

Kidney function tests, including a measurement of BUN, 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 produced due to the breakdown of proteins in the body.

The kidneys filter urea out of the blood so 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 indicate 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 this test?

BUN is usually measured as part of the BMP or CMP. These tests involve eight and 14 measurements, respectively, and provide insight into multiple bodily systems, including kidney function.

A panel of tests with a BUN measurement may be appropriate if you have kidney disease signs and/or symptoms. 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 the benefits of routine screening outweigh its downsides, including the costs of testing and the 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 to monitor your situation and current kidney function.

Finding a Blood Urea Nitrogen Test

How can I get a blood urea nitrogen test?

A doctor normally prescribes testing for BUN, and the test is performed using a sample of blood drawn from a vein in your arm. The blood draw normally occurs 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 both the BMP and CMP.

Can I take the test at home?

At-home tests are available that include a measurement of BUN. These tests do not typically measure BUN alone but involve a few additional measurements related to kidney function. For an at-home BUN test, you prepare a blood sample from your 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 from a vein.

How much does the test cost?

BUN testing does not have a set cost. Instead, the cost depends on where the test is performed 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.

A BUN test’s total cost includes several components, including charges for an office visit, a blood draw by a technician, and laboratory analysis. Health insurance often covers these costs if the test has been prescribed for you by your doctor.

Check with your insurance company and doctor’s office for more detailed information about test costs, and 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 of shipping your sample.

Taking a Blood Urea Nitrogen Test

Since this test measures urea nitrogen in the blood, testing requires a blood sample 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, tell your doctor about any prescription drugs, over-the-counter medications, and/or dietary supplements 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 preparations, including fasting, are not normally needed for a BUN test alone. However, if BUN is being tested with other measurements, such as in a BMP or CMP, you will likely be instructed to fast for eight to 12 hours before the blood draw.

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

During the test

After you are seated, a technician will tie an elastic band around the top part of your arm 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, 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 will be finished.

The blood draw procedure usually takes just a few minutes, during which you may feel temporary pain or a stinging sensation.

You’ll use an included device with a very small needle to prick your fingertip for an at-home test. Next, you put a drop of blood on a test strip that is 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 it tends to go away quickly if this occurs.

Usually, you can 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 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 access 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. The results are usually available online or through a smartphone app.

Interpreting test results

The test report should include a line for BUN that shows the level found in your sample as well as the laboratory’s reference range. BUN is typically reported 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 BUN as eight to 20 mg/dL. However, this range is not universal. Labs can use different methods to measure BUN or report BUN in different units, 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 BUN. 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, symptoms, 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 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 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 BUN levels can signify malnutrition, lack of protein in the diet, and liver disease. Therefore, other tests included in a panel test, like the CMP, may provide helpful information for understanding the significance of low BUN.

Some questions that may be helpful when you review your BUN 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?

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