December 7, 2023
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Why Is the Blood Urea Nitrogen (BUN) Test Important?

What is a BUN test

The blood urea nitrogen (BUN) test is the blood test that indicates the health of your kidneys. A BUN test measures the urea nitrogen levels in your blood. This article will inform you about the importance of BUN for your health. Abnormal (High or low) levels of BUN can show several possible diseases, such as kidney failure or damage.

What is a BUN test?

The blood urea nitrogen test is the test that can determine the amount of urea nitrogen in your blood. Urea nitrogen is a waste substance that your body produces. When you take proteins in your diet, your liver breaks them into your food and develops ammonia, which includes nitrogen. Nitrogen reacts with other substances, including carbon, oxygen, and hydrogen to produce urea (a waste product). This waste substance enters your blood through the liver and reaches your kidneys, which separate from your blood. After that, BUN is eliminated from your body through urine.

Urea nitrogen levels in the blood are one of the significant factors that can help your provider to know about kidney conditions. Generally, if your kidneys are healthy, you will have low amounts of urea nitrogen levels in your blood. A high BUN level tells that your kidney cannot filter accurately, leading to kidney failure.

Why do I need a BUN test?

A blood urea nitrogen (BUN) test may recommend to you when you have the following conditions:

  • A provider may consider that you have kidney failure or disease.
  • To diagnose kidney functions, specifically in the case of these diseases, including high blood glucose levels or high blood pressure.
  • To monitor the treatment for kidney disease or dialysis.

This test may be suggested for your routine checkup as included in a group of tests such as a comprehensive metabolic panel (CMP) or basic metabolic panel (BMP) blood test. With these blood tests, the BUN test may help to detect various diseases, such as liver failure, congestive heart failure, or urinary tract obstruction. But the abnormal blood urea nitrogen test individually does not indicate that you have any of these diseases.

The early stages of kidney disease often do not have signs and symptoms, but you may have a high chance of developing it due to

  • Heart disease
  • Diabetes
  • Family history of kidney disease
  • Increased blood pressure

Symptoms of later-stage kidney disease

Symptoms of later-stage kidney disease

You may need to take a BUN test if you have symptoms of later-stage kidney disease. These include:

  • Frequent urination
  • Cloudy urine
  • Blood in your urine
  • Swelling in your hands, legs, ankles, near your eyes, face, or abdomen.
  • Fatigue or tiredness
  • Restless legs while sleeping
  • Decreased appetite

The Procedure of Blood Urea Nitrogen Test 

The Procedure of Blood Urea Nitrogen Test

You will need to provide a blood sample for the BUN test. A provider will inject a small needle into a vein of your arm to collect the blood sample. You may experience pain or discomfort during needle injections. Your blood sample will be stored at the laboratory to examine BUN levels. You may receive your test results within at least one or two days.

What are the preparations required for this test? 

A blood urea nitrogen test does not require specific preparation. If a provider asks for a BUN test, fasting is not needed. But if you have additional blood tests to order, your provider may recommend you fast (avoiding eating or drinking) before the test. If you take any antibiotics or medications for a long time, you may need to inform your provider.

BUN Normal Range 

The test results of BUN are expressed in milligrams per deciliter (mg/dL) or millimoles per liter (mmol). The normal range of BUN may depend on several factors, which include age, sex, medical history, and others. Following are the recommendations of BUN ranges according to different age groups, which include:

  • For children aged between 1 and 17 years: The normal BUN level is between 7 and 20 mg/dL.
  • For adult women: The recommended blood urea nitrogen level ranges from 6 to 21 mg/dL.
  • For adult men: The normal BUN level starts from 8 to 24 mg/dL.

The test results may be slightly different among laboratories. Each lab may use different reference ranges or techniques. You can request an online medical consultation from a provider if you need to know your test result.

What do high BUN levels in the blood test indicate? 

High blood urea nitrogen levels may show that your kidneys are not healthy.

What does high BUN levels in the blood test indicate

Here are the causes of high BUN levels that may lead to kidney damage or failure:

  • Dehydration (Not getting recommended water or fluids intake)
  • Obstruction in the urinary tract (difficulty urinating due to blockage)
  • Congestive heart failure (a condition in which the heart does not supply blood to your body compared to normal)
  • High protein intake
  • Stress
  • Heart attack
  • Shock
  • Burn injuries
  • Gastrointestinal bleeding (a condition in which bleeding shows up in your digestive system, including the stomach, intestines, etc.)
  • Use of specific medication for a long time

If your test results indicate high urea nitrogen levels in your blood, you should discuss it with an online provider.

Low BUN levels 

Low BUN levels are often not found in people. If you have low urea nitrogen levels in the blood, it may be due to the following:

  • Excess intake of fluid
  • Not taking enough protein
  • Liver disease

BUN/Creatinine Ratio

A healthcare provider may also recommend a creatinine test to diagnose the condition of your kidney’s health. Creatinine is the waste substance that develops from your muscles and clears out from your kidneys. A provider often compares the BUN levels with the creatinine to get more comprehensive information about the working of your kidneys, also called the BUN/Creatinine ratio.

High Creatinine levels also tell that your kidneys fail to eliminate this waste substance from your blood. The recommended range of BUN/creatinine lies between 10 to 1 and 20 to 1. A higher ratio than this may indicate dehydration, gastrointestinal bleeding, or congestive heart failure due to a lack of blood supply to your kidneys. A low Creatinine/BUN ratio may lead to liver disease or malabsorption.


Urea nitrogen is a waste substance produced by your liver during the breakdown of proteins. A blood urea nitrogen (BUN) test may show kidney damage or failure but does not tell the exact cause of it. If you have the symptoms of later-stage kidney disease, you should take immediate action and consult an online professional provider for treatment.

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