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Blood Urea Nitrogen (BUN) Test

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What is a Blood Urea Nitrogen (BUN) test?

Urea nitrogen is a waste product that is formed when the liver processes protein. This urea is then excreted by the kidneys. A blood urea nitrogen (BUN) test measures the level of this waste product in the blood. Accumulation of waste products in the bloodstream indicates that the kidneys are unable to perform adequately. However, excessive breakdown of protein can also raise BUN levels.

Why is it conducted?

This test is generally conducted to measure how well the kidneys are functioning. In this case, a creatinine test may be ordered simultaneously as the BUN-creatinine ratio assists in differential diagnosis. It is also a part of the metabolic panel tests that are carried out to assess the body’s metabolism in general. It is also a useful test for assessing dehydration in patients.

Who should go for it?

  • Persons who exhibit symptoms of kidney disease, such as, swollen ankles, puffy eyes, less urine, are often advised this test.
  • Persons who have already been diagnosed with kidney disease, heart failure or heart attack may be advised this test to monitor treatment.
  • Persons suffering from diabetes or high blood pressure are advised to have this test to ensure that the kidneys are working properly.
  • People who are acutely ill may be requested this test as it helps to assess the body’s chemical processes.
  • Persons who have vague symptoms may also be advised this test.
  • Persons on dialysis are routinely ordered this test to monitor its effectiveness.
  • People who are about to begin certain medications that may have a detrimental impact on the kidneys are also advised this test.


This is a simple blood test that does not require any special preparation. However, one should avoid a high protein diet, especially meat, from 24 hours prior to the test. A technician will draw blood from the inside of the elbow.

Interpretation of results 

Normal range for the BUN test is from 6 to 20 mg/dL, though it will be lower in women and infants. It is likely to be slightly higher for seniors above 60 years old.

Certain medications, such as antibiotics and steroids, can affect the level of urea nitrogen in the body. These should be taken into consideration when interpreting the results. Besides this, the use of diuretics may lower the fluid level in the body and show high BUN levels. Conversely, excess drinking of water or over-hydration may give low BUN results. Other than this, diet also plays a role. A diet high in protein will yield a high BUN result whereas a diet low in protein will lower the urea levels in the body.

High levels of urea nitrogen may be due to kidney disease, obstruction in the urinary tract, shock and severe burns. Besides this, it is also likely to rise in the case of a heart attack or due to congestive heart failure(less blood flow to kidneys). Bleeding in the gastrointestinal tract can also cause urea levels to rise due to the presence of protein in the blood.

Low levels are likely to occur in the case of advanced liver disease, rhabdomyolysis (breakdown of muscles) and SIAD (syndrome of inappropriate antidiuresis). It is normal for BUN levels to be low in later pregnancy. Another reason for low levels can be malnutrition or malabsorption syndrome.

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Written by: healthplus24.com team

Date last updated: February 03, 2015

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