Blood Urea Nitrogen (BUN)

Clinical definition of the Blood Urea Nitrogen test
The blood urea nitrogen (BUN test) is a measure of the amount of nitrogen in the blood in the form of urea, and a measurement of renal function. Urea is a waste product of the breakdown of protein. It is secreted by the liver, and removed from the blood by the kidneys.
A BUN test is usually done to check for the normal working of the kidneys.

  • The BUN level rises if the kidneys are unable to remove urea from the blood normally. Heart failure, dehydration, or a diet high in protein can also increase the BUN level.
  • Reduction of the BUN level may occur in case of a liver disease or damage. A low BUN level can occur normally in the second or third trimester of pregnancy.

A blood creatinine test may be done along with a BUN test since the level of creatinine in the blood also indicates the working of the kidneys. The BUN:creatinine ratio may be assessed to check for problems, such as dehydration.

Why is the Blood Urea Nitrogen test done?
The blood urea nitrogen (BUN) test is done to assess or monitor the following

  • Check the normal functioning of the kidney in patients with diabetes, congestive heart failure, and myocardial infarction (heart attack)
  • Presence or progress of kidney or liver disease
  • Effect of a treatment to the kidney or liver disease
  • Monitor the effectiveness of kidney dialysis
  • Blockage of urine flow
  • Abnormal loss of water from the body (dehydration)
  • Mental confusion- since patients with kidney failure are sometimes disoriented and confused
  • Recovery from severe burns- since the body uses larger than normal amounts of protein following serious burns

What are the common signs/symptoms when the Blood Urea Nitrogen test is done?
Symptoms of a kidney related disorder

  • Poor appetite
  • Fatigue
  • Lack of concentration
  • Trouble sleeping
  • Swelling or puffiness especially around the eyes or in the face, ankles, hands, feet abdomen wrists, abdomen and thighs
  • Foamy, bloody, or dark-colored urine
  • Reduced urine output or change in the frequency of urination
  • Discomfort during urination (burning sensation)
  • Mid-back pain
  • Pain below the ribs (location of the kidneys)
  • High blood pressure

Who should do the Blood Urea Nitrogen test (Target population)?
Persons showing the above signs & symptoms of a kidney disorder or those undergoing a treatment for kidney or liver disease.

What should I do before the Blood Urea Nitrogen (BUN) test?

Specimen type

Specimen collection procedure

Preparatory instructions before the test *


(Blood Sample)


(Collection of blood from a vein, usually from the arm)

No Fasting Required.

No other special preparations required.

*Subjects suffering from any illness or on oral or injectable medications are advised to consult their physician prior to requesting any tests or procedures.

How do I interpret my Blood Urea Nitrogen test (BUN) results?

Reference Range*






07 to 18 mg/dL



07 to 18 mg/dL


Child (Age)

0 - 4 days

3 - 19 mg/dl


5 days - 2 yrs

6 - 17 mg/dl


3 - 12 yrs

8 - 18 mg/dl


13 - 18 yrs

9 - 21 mg/dl


Bun: Creatinine  Ratio

Prerenal Azotemia

Ratio (>20:1)

With normal creatinine

Postrenal Azotemia

Ratio (>20:1)

With elevated creatinine

‘*A Reference range is a set of values which helps the healthcare professional to interpret a medical test. It may vary with age, gender, and other factors. Reference ranges may also vary between labs, in value & units depending on instruments used and method of establishment of reference ranges’

Diseases/conditions related to the Blood Urea Nitrogen (BUN) test

  • Azotemia
  • Dehydration
  • Shock
  • Acute or chronic disease of the kidney
  • Prerenal azotemia

Other tests related to the Blood Urea Nitrogen (BUN) test

  • Urine Routine
  • Microalbumin
  • Creatinine
  • Creatinine Clearance
  • eGFR
  • Comprehensive Metabolic Panel
  • Basic Metabolic Panel

Synonyms : eGFR
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BUN (Blood Urea Nitrogen)