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Dr. Shreya Gupta
BDS, MDS - Oral and Maxillofacial Pathology
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Dr. Ashish Ranjan
MBBS, MD (Pharmacology)
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Blood Urea Nitrogen (BUN)

Also known as Urea Nitrogen
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Male, Female

Understanding Blood Urea Nitrogen (BUN)

What is Blood Urea Nitrogen (BUN)?


Blood urea nitrogen test is also known as urea nitrogen test or BUN. This test is done to evaluate the overall health of the kidney, to diagnose kidney diseases, and to monitor the treatment of kidney diseases such as dialysis.



What is Blood Urea Nitrogen (BUN) used for?

The Blood Urea Nitrogen test is done:

    • As a part of the routine comprehensive check-up

    • As a part of the basic metabolic panel

    • In case of signs and symptoms of kidney disease

    • In case a patient is undergoing treatment for kidney disease

What does Blood Urea Nitrogen (BUN) measure?

A Blood Urea Nitrogen (BUN) test measures the levels of urea nitrogen in the blood. Blood urea is a waste product that is formed in the liver when you eat food and the protein is metabolized into amino acids. This process leads to the production of ammonia that is further converted into urea. Both ammonia and urea are nitrogenous compounds. Your liver releases urea into the blood which is then carried out to the kidneys. In the kidneys, urea is filtered from the blood and flushed out of the body via urine. This is a continuous process, so a small amount of urea nitrogen always remains in the blood.

In the case of a kidney or liver disease, there is a change in the amount of urea present in the blood. If your liver produces urea in an increased amount or if there is any problem in kidney functioning, there might be difficulty in filtering out the waste products from the blood, which can result in increased urea levels in the blood.

Interpreting Blood Urea Nitrogen (BUN) results


The reference range for BUN is as follows:



Reference range in mg/dL

0 - 1 week

3 - 25

1 week - 1 year

4- 19

1 - 12 years

5 - 18

12 - 60 years

6 - 20

60 - 90 years

8- 23

> 90 years

10 - 31



Reference range may vary from lab to lab*


Answers to Patient Concerns & Frequently Asked Questions (FAQs) about Blood Urea Nitrogen (BUN)

Frequently Asked Questions about Blood Urea Nitrogen (BUN)

Q. Is there any preparation required before the test?

Inform the doctor about the medications you may be taking. No other specific preparations are usually required before this test.

Q. What other tests can be advised by the doctor along with BUN test?

The BUN test is advised along with a creatinine test or renal panel in case a doctor suspects kidney diseases in the patient.

Q. What are the signs and symptoms of kidney dysfunction?

The signs and symptoms of kidney dysfunction include swelling around eyes or in the face, wrists, abdomen, thighs or ankles, fatigue, lack of concentration, poor appetite, and difficulty sleeping. Ther other symptoms can be foamy or bloody or coffee-colored urine, decrease in the amount of urine, discomfort in urinating (e.g., feeling of burning sensation while urinating or passage of discharge while urinating), change in frequency of urination, mid back pain below the ribs, and high blood pressure.

Q. What do abnormal results of BUN mean?

The increased levels of BUN are seen in case of impaired kidney function which may be due to acute or chronic kidney disease, damage or failure, and conditions causing obstruction of urine flow and dehydration. Along with that, levels of BUN can increase when there is decreased blood flow to the kidneys such as in case of congestive heart failure, shock, stress, recent heart attack or severe burns. The levels of BUN also rise when there is more than normal breakdown of protein, increase in protein diet or gastrointestinal bleeding. The decreased levels of BUN are seen in case of severe liver disease, malnutrition, and over hydration.

Q. How is the blood sample taken?

The healthcare provider takes a blood sample from the arm. The site from where the blood is to be withdrawn is cleaned with a swab of rubbing alcohol. This is then followed by inserting a small needle which has a tube attached to it for collecting blood. Once the sufficient blood for analysis is withdrawn, the needle is removed. The site is then covered with a gauze pad.

Q. Is there any risk associated with the withdrawal of blood sample procedure?

As such there is no risk but in few cases, bruising, bleeding, and infection at the puncture site can be seen. In very few cases, there can be swelling of the vein after the blood is withdrawn.
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