Home Health A-Z Blood Urea Nitrogen (BUN Test): Preparation, Results & Risk Factors

Blood Urea Nitrogen (BUN Test): Preparation, Results & Risk Factors

Verified By Apollo Doctors June 10, 2021 9027 0
Blood Urea Nitrogen (BUN Test)
Blood Urea Nitrogen (BUN Test)


The BUN test or Blood Urea Nitrogen Test is a common blood test performed to check the proper functioning of the kidneys. It essentially measures the urea nitrogen count in the blood to find out ailments related to it. 

What is BUN Test?

As already mentioned, BUN test is a diagnostic procedure to check the health of your kidneys. The liver breaks down the proteins in your food — and while doing so, the liver creates blood urea nitrogen, also called BUN. Your liver releases this BUN into your blood, and it ends up eventually in your kidneys. Your kidneys, when they are healthy, remove the BUN, generally leaving a small amount of it in your blood. However, for the most part, your healthy kidneys discard it by flushing it out of your body through urine.

However, if your kidneys fail to function properly, the level of nitrogen and urea in your blood will rise. If you need to know the exact amount of urea currently present in your blood, you should undergo a Blood Urea Nitrogen test, which is called BUN, in short.

The level of urea and nitrogen will be higher in cases of kidney problems, heart diseases, and dehydration. In contrast, the BUN level tends to be lower in patients suffering from liver diseases. The other names for the BUN test are the Urea Nitrogen test and Serum BUN.

What is the BUN test used for?

A BUN test can help diagnose a disorder related to Kidney. This test is part of a series of tests known as comprehensive metabolic panel. 

Why do I need a BUN test?

A BUN test will be recommended as part of a routine checkup or if the healthcare provider suspects kidney disease. Generally, kidney diseases will not show any early indicators. So, you will have to look if you have a hereditary kidney issue, high blood pressure, heart disease, or diabetes. The test may also be done if you have a feeling to urinate frequently, fatigue, itching, trouble sleeping, muscle cramps, or swelling in legs and ankles. 

How to Prepare for the BUN Test?

You do not need to undergo any special preparation before a BUN test. You should only follow the instructions given by the doctor who recommended the test. 

However, you should inform your doctor about all the medications you are currently taking to avoid complications. 

Some medicines, like tetracycline, methyldopa, and carbamazepine, can raise your BUN level, and hence, your doctor may suggest stopping these medicines for the time being. You also need to limit your daily intake of fish, meat, and other protein-rich foods at least 24 hours before this test.

Taking the BUN test.

You need to give a sample of your blood to check the BUN. The healthcare provider may take it from your vein or finger, depending upon if it is an at-home test or a lab test. 

Before the test

Before scheduling the test, you must visit the healthcare provider to check whether you need to undergo any dietary or medicinal changes. Some food and medicine may interfere in getting the right values during the test. BUN test alone, normally does not require fasting. But if it is done along with other tests, and if those tests demand fasting, you may have to fast for 8 to 12 hours. You can clarify this with your healthcare provider. 

During the Test

During a lab test, the provider may tie a plastic band around the top area of your arm to increase blood flow in the vein. Then they will draw an adequate amount of blood using a needle after cleaning the site with an antiseptic. This sample will be used to test in the laboratory. During the at-home test, a small needle will be used to prick the finger and a drop of blood will be taken to send to the lab for testing.

After the test

After the test you can apply pressure on the site where blood was drawn, to stop further bleeding. If you are asked to fast before the test, you can bring some snacks to have after the test. There shouldn’t be any side effects or complications associated with this test.

What to Expect from the BUN Test?

Only a tiny amount of your blood will be drawn for the BUN test. A lab technician will tie a band around your arm to dilate your veins for drawing the blood with a sterile syringe. You will experience mild pain, like a stinging sensation during this process, which should subside very soon. A bandage will be applied to this punctured area of your skin to stop the bleeding and heal it quickly. 

Subsequently, your blood sample will be tested with the necessary reagents to assess the urea and nitrogen levels in your blood. You can leave immediately after your blood sample is taken unless you experience any physical problem after the test.

Possible Results from Your BUN Test

Receiving Test Results

A lab test result generally takes a few days to reach the patient. You may get it online or as a hardcopy. If the test was taken using a kit at home, it might take a few more extra days to get the results. 

Interpreting test results 

The result will have a line of reference given by the lab and the actual count of the sample taken from you. The BUN is measured in milligrams per deciliter and a count between 8 to 20mg/dl is considered normal. This standard rate can vary slightly from lab to lab. It is always better to take the result to a doctor to check for ailments. 

An elevated BUN result is not just due to kidney problems but can be due to excessive protein content in body, dehydration, burns or due to certain medications. BUN levels alone will not affect kidney functioning. It has to be studied along with other measurements like creatinine, a breakdown product of muscle, filtered by kidney. 

If the BUN level is very low, it can be due to malnutrition, protein deficiency or liver issue. So, doctors usually recommend taking a panel test so that they can compare all the measurements and diagnose the problem. 

Are the test results accurate?

BUN test results are almost accurate in most cases. There are protocols existing to avoid errors and getting the right values. This may help deduce a correct interpretation of the blood sample.

Do I need to do a follow-up test?

If the result shows abnormal counts, you will have to check with the doctor to find out underlying causes. As the doctor recommends, you may have to conduct further tests and treat the causal agent of the abnormality in BUN counts. For this follow-up appointment is necessary. 

When to See a doctor?

If your BUN test report shows a much higher value than the normal range of your age group, it may be a sign of some underlying health conditions. You may be suffering from some cardiac problem, kidney failure, dehydration, injury in your gastrointestinal tract, or a blockage in your urinary tract. 

Abnormally high BUN levels may be due to the reactions of some medications that you are taking for curing other ailments. If you see a much lower BUN value than the normal range in your report, it may signify that you are suffering from liver damage or malnutrition. 

If you eat too little protein-rich foods or drink too much water, your BUN level may be lower than expected as well. However, the BUN levels may also become abnormal during pregnancy. 

It is best to see a doctor when you find a higher or lower BUN value in your BUN test report to ascertain the exact cause of this result.

What high BUN levels can mean?

As mentioned earlier, an elevated BUN level may not just indicate issues with kidney functioning. Healthcare providers suggest other tests along with BUN tests to find out the real reason behind this elevation. It can also be due to dehydration or overhydration, burn injuries, stress, anxiety, shock, cardiac issues, bleeding in the gastro intestinal organs or malnutrition.

Creatinine Test

Creatinine is a waste product from muscles which is filtered by kidneys. If the creatinine level is high, it means that the kidney is not filtering properly. Comparing the levels of BUN and creatinine gives the healthcare provider an idea regarding the functioning of the kidney. The ideal ratio of BUN to creatinine should be 10-to-1 and 20-to-1. A ratio above this could mean a reduced blood flow to the kidneys and it can be due to heart issues, dehydration or bleeding in gastro-intestinal organs. A ratio below this range could be due to liver disease or malnutrition. 


Frequently Asked Questions (FAQs)

What level of BUN indicates Kidney failure?

There is no fixed range of BUN that indicates kidney failure. The range 8 to 20mg/dl is considered normal. A more precise result can be derived by comparing the BUN value with creatinine or other important measurements. 

What does BUN mean?

BUN refers to Blood Urea Nitrogen test which helps in finding out if the kidneys are functioning properly. 

What is a dangerously high BUN level? 

The normal range of BUN is 8 to 20mg/dl. Anything above or below this range requires medical attention and your healthcare provider may suggest tests to confirm the severity of your case.

What does high BUN mean?

Higher levels of BUN refer to kidney issues. It may also be due to other issues like gastro-intestinal bleeding, cardiac issues, dehydration/overhydration, stress or burns. The exact cause can be diagnosed by comparing the BUN results with other test results. 

How do you fix high BUN levels?

 It is always recommended to seek the help of an expert if your BUN levels have gone up. But generally, treating the underlying cause of the abnormal BUN can lower the levels significantly. For example, if the reason for elevated BUN is dehydration, increasing the water intake can help. 

What causes high BUN levels?

High BUN levels can be due to improper functioning of kidneys, dehydration/overhydration, injuries from burns, excessive protein intake, cardiac issues or gastro-intestinal organ injuries.  

Is the BUN test a sign of kidney damage?

The BUN test is not only meant to detect kidney problems, as there are multiple reasons for the increase in the urea and nitrogen levels in your blood. So, you need not worry about your kidneys’ health when your doctor recommends conducting a BUN test. 

How can kidney failure be confirmed through the BUN test?

As the BUN test is usually done along with a creatinine test, your doctor can compare both results to determine your kidneys’ condition. The presence of a large amount of creatinine with a high BUN level in your blood can imply that your kidneys are not working properly.

How does the BUN test contribute to your kidney treatment?

In cases where the patients undergo peritoneal dialysis and hemodialysis, doctors need the current blood test reports to monitor the treatment and response. The BUN test report provides the levels of urea and nitrogen in patients’ blood and also shows the progress in their conditions after dialysis. Hence, doctors can decide whether to continue with further rounds of dialysis. 

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At Apollo, we believe that easily accessible, reliable health information can make managing health conditions an empowering experience. AskApollo Online Health Library team consists of medical experts who create curated peer-reviewed medical content that is regularly updated and is easy-to-understand.

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