What Should I Do If My Bun/Creatinine Ratio Is High

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Blood Urea Nitrogen (BUN) Test

This information does not replace the advice of a doctor. Ignite Healthwise, LLC, disclaims any warranty or liability for your use of this information. Your use of this information means that you agree to the Terms of Use . Learn how we develop our content .

BUN (Blood Urea Nitrogen)

A BUN, or blood urea nitrogen test, can provide important information about your kidney function. The main job of your kidneys is to remove waste and extra fluid from your body. If you have kidney disease, this waste material can build up in your blood. Over time, this may lead to serious health problems, including high blood pressure, anemia, and heart disease.

The BUN test measures the amount of urea nitrogen in your blood. Urea nitrogen is a waste product that your kidneys remove from your blood. Higher than normal BUN levels may be a sign that your kidneys aren’t working well.

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.

Other names for a BUN test: Urea nitrogen test, serum BUN

What is it used for?

A BUN test is often part of a series of tests called a comprehensive metabolic panel. It can help diagnose or monitor a kidney disease or disorder.

Why do I need a BUN test?

Your health care provider may order a BUN test as part of a routine check-up or if you have or are at risk for a kidney problem. Early kidney disease usually does not have any signs or symptoms. You may be more likely to develop kidney disease if you have:

  • Family of kidney problems
  • Diabetes
  • High blood pressure
  • Heart disease

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

  • Needing to urinate (pee) more often or less often than usual
  • Itching
  • Fatigue
  • Swelling in your legs, feet, or ankles
  • Muscle cramps
  • Trouble sleeping

What happens during a BUN test?

A health care professional will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out. This usually takes less than five minutes.

Will I need to do anything to prepare for the test?

Usually there is no special preparation necessary for a BUN test. But if your provider has ordered other tests on your blood sample, you may need to fast (not eat or drink) for several hours before the test. Your provider will let you know if there are any special instructions to follow.

Are there any risks to the test?

There is very little risk to having a blood test. You may experience slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.

What do the results mean?

Normal BUN levels can vary, but generally a high level of blood urea nitrogen is a sign that your kidneys are not working well. But abnormal results don’t always mean that you have a medical condition that needs treatment.

Higher than normal BUN levels can also be caused by dehydration (too little fluid in your body), burns, certain medicines, a high protein diet, or other factors, including your age. BUN levels normally increase as you get older. To learn what your results mean, talk to your health care provider.

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

References

  1. Testing.com [Internet]. Seattle (WA): OneCare Media; c2022. Blood Urea Nitrogen;; [modified 2021 Nov 9; cited 2021 Dec 31]; [about 8 screens]. Available from: https://www.testing.com/tests/blood-urea-nitrogen-bun/
  2. Lyman JL. Blood urea nitrogen and creatinine. Emerg Med Clin North Am [Internet]. 1986 May 4 [cited 2017 Jan 30]; 4(2):223–33. Available from: https://www.ncbi.nlm.nih.gov/pubmed/3516645
  3. Mayo Clinic [Internet]. Mayo Foundation for Medical Education and Research; c1998-2022. Blood Urea Nitrogen (BUN) Test; [cited 2021 Dec 31]; [about 3 screens]. Available from: http://www.mayoclinic.org/tests-procedures/blood-urea-nitrogen/home/ovc-20211239
  4. Mayo Clinic [Internet]. Mayo Foundation for Medical Education and Research; c1998-2022. Chronic Kidney Disease; [cited 2021 Dec 31]; [about 3 screens]. Available from: https://www.mayoclinic.org/diseases-conditions/chronic-kidney-disease/symptoms-causes/syc-20354521
  5. National Heart, Lung, and Blood Institute [Internet]. Bethesda (MD): U.S. Department of Health and Human Services; Blood Tests [; cited 2021 Dec 31]; [about 19 screens]. Available from: https://www.nhlbi.nih.gov/health-topics/blood-tests
  6. National Institute of Diabetes and Digestive and Kidney Diseases [Internet]. Bethesda (MD): U.S. Department of Health and Human Services; Kidney Disease; [cited 2021 Dec 31]; [about 7 screens]. Available from: https://www.niddk.nih.gov/health-information/kidney-disease
  7. National Institute of Diabetes and Digestive and Kidney Diseases [Internet]. Bethesda (MD): U.S. Department of Health and Human Services; National Kidney Disease Education Program: Your Kidney Test Results; [updated 2013 Feb; cited 2017 Jan 30]; [about 3 screens]. Available from: https://www.niddk.nih.gov/-/media/Files/Health-Information/Health-Professionals/Kidney-Disease/Your_Kidney_Test_Results_EN.pdf
  8. National Kidney Foundation [Internet]. New York: National Kidney Foundation Inc., c2022. About Chronic Kidney Disease; [cited 2017 Jan 30]; [about 3 screens]. Available from: https://www.kidney.org/kidneydisease/aboutckd
  9. National Kidney Foundation [Internet]. New York: National Kidney Foundation Inc., c2022. Understanding Lab Values; [cited 2017 Jan 30]; [about 2 screens]. Available from: https://www.kidney.org/kidneydisease/understandinglabvalues
  10. University of Rochester Medical Center [Internet]. Rochester (NY): University of Rochester Medical Center; c2022. Health Encyclopedia: Blood Urea Nitrogen; [cited 2017 Jan 30]; [about 3 screens]. Available from: https://www.urmc.rochester.edu/encyclopedia/content.aspx?contenttypeid=167&contentid=urea_nitrogen_serum
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Related Health Topics

  • Chronic Kidney Disease
  • Diabetic Kidney Problems
  • Kidney Diseases
  • Kidney Failure
  • Kidney Tests

Blood Urea Nitrogen (BUN) Test

A blood urea nitrogen (BUN) test measures the amount of nitrogen in your blood that comes from the waste product urea. Urea is made when protein is broken down in your body. Urea is made in the liver and passed out of your body in the urine.

A BUN test is done to see how well your kidneys are working. If your kidneys are not able to remove urea from the blood normally, your BUN level rises. Heart failure , dehydration , or a diet high in protein can also make your BUN level higher. Liver disease or damage can lower your BUN level. A low BUN level can occur normally in the second or third trimester of pregnancy.

Blood urea nitrogen to creatinine ratio (BUN:creatinine)

A BUN test may be done with a blood creatinine test. The level of creatinine in your blood also tells how well your kidneys are working—a high creatinine level may mean your kidneys are not working properly. Blood urea nitrogen (BUN) and creatinine tests can be used together to find the BUN-to-creatinine ratio (BUN:creatinine). A BUN-to-creatinine ratio can help your doctor check for problems, such as dehydration, that may cause abnormal BUN and creatinine levels.

Why It Is Done

Why It Is Done

A BUN test is done to:

  • See if your kidneys are working normally.
  • See if your kidney disease is getting worse.
  • See if treatment of your kidney disease is working.
  • Check for severe dehydration. Dehydration generally causes BUN levels to rise more than creatinine levels. This causes a high BUN-to-creatinine ratio. Kidney disease or blockage of the flow of urine from your kidney causes both BUN and creatinine levels to go up.

How To Prepare

How To Prepare

Do not eat a lot of meat or other protein in the 24 hours before having a BUN test.

How It Is Done

How It Is Done

A health professional uses a needle to take a blood sample, usually from the arm.

How It Feels

How It Feels

When a blood sample is taken, you may feel nothing at all from the needle. Or you might feel a quick sting or pinch.

Risks

There is very little chance of having a problem from this test. When a blood sample is taken, a small bruise may form at the site.

Results

Normal

Each lab has a different range for what’s normal. Your lab report should show the range that your lab uses for each test. The normal range is just a guide. Your doctor will also look at your results based on your age, health, and other factors. A value that isn’t in the normal range may still be normal for you.

High values

  • A high BUN value can mean kidney injury or disease is present. Kidney damage can be caused by diabetes or high blood pressure that directly affects the kidneys. High BUN levels can also be caused by low blood flow to the kidneys caused by dehydration or heart failure .
  • Many medicines may cause a high BUN. Be sure to tell your doctor about all the nonprescription and prescription medicines you take.
  • A high BUN value may be caused by a high-protein diet, Addison’s disease , or tissue damage (such as from severe burns), or from bleeding in the gastrointestinal tract.
  • High BUN-to-creatinine ratios occur with sudden (acute) kidney problems, which may be caused by shock or severe dehydration. A very high BUN-to-creatinine ratio may be caused by bleeding in the digestive tract or respiratory tract .
See Also:  What Does A Popped Blood Vessel Look Like

Low values

  • A low BUN value may be caused by a diet very low in protein, by malnutrition, or by severe liver damage.
  • Drinking too much liquid may cause overhydration and cause a low BUN value.
  • Women and children may have lower BUN levels than men because of how their bodies break down protein.
  • A low BUN-to-creatinine ratio may be caused by a diet low in protein, a severe muscle injury called rhabdomyolysis , pregnancy, cirrhosis , or syndrome of inappropriate antidiuretic hormone secretion (SIADH).

Current as of: May 13, 2023

Author: Ignite Healthwise, LLC Staff

Clinical Review Board
All Healthwise education is reviewed by a team that includes physicians, nurses, advanced practitioners, registered dieticians, and other healthcare professionals.

This information does not replace the advice of a doctor. Ignite Healthwise, LLC, disclaims any warranty or liability for your use of this information. Your use of this information means that you agree to the Terms of Use . Learn how we develop our content .

To learn more about Ignite Healthwise, LLC, visit webmdignite.com .

© 2024 Ignite Healthwise, LLC. Healthwise, Healthwise for every health decision, and the Healthwise logo are trademarks of Ignite Healthwise, LLC.

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Dr Narelle Bleasel FACD
Dr Narelle Bleasel FACD

Dermatologist in Battery Point, Australia

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