What is BUN test?

What is the importance of a BUN test?

A blood urea nitrogen or BUN test reveals about the kidney function. This test helps in measuring the levels of urea nitrogen in the blood. In a properly functioning kidney all metabolic waste like excess fluids, salts, minerals, toxins, and even urea etc. are removed from the blood during the filtration process. However, if the kidney function is impaired than the accumulation of all waste byproducts is not done effectively and hence buildup of toxins occurs within the body. It further causes high blood pressure, anemia and cardiac issues. Since kidneys control the blood pressure and production of blood cells in the body.

So in case of malfunctioned kidneys presence of urea nitrogen in the blood reveals the sign of any kidney disease. Moreover, BUN helps in early detection of the kidney disease when symptoms even might not have appeared at times. Early diagnosis of the kidney disease increases treatment efficacy chances. Urea nitrogen test and serum BUN are few other names of this test.

The process of urea formation and its removal from the body:

The liver of the human body is responsible for the production of ammonia which contains nitrogen. It further breaks down into the protein which is used as building blocks by the cells. The free nitrogen combines with other available free waste byproducts like carbon, hydrogen, and oxygen to form urea. This urea then reaches the kidneys from the liver via blood. If the kidneys are healthy then removal of this urea is initiated by them via filtration process. Finally, urea passes out of the body in urine. In a BUN test, level of urea in the urine suggests if kidneys are working properly or not. If the level of urea is within the normal range then everything seems fine however in case the levels are high it indicates a malfunction of the kidneys.

High levels of BUN can arise because of high protein diet, dehydration, and heart failure. However, low levels of BUN can occur because of liver disease or damage. But during the second trimester of pregnancy, it is normal to have low levels of a BUN.

BUN test

Why is a BUN test done?


A BUN test is an important component of a set of tests known as the comprehensive metabolic panel, which can help diagnose any kidney disorder or disease. Your physician might suggest to undergo BUN test as a routine checkup or to rule out kidney issues if he suspects any symptoms.

There are few factors which make a person prone to more risks of developing any kidney disease like hypertension, diabetes, cardiac issues, and any family history of kidney disease. Besides BUN other tests like GFR or eGFR, and creatinine level test etc. are also done to confirm kidney disease.

Further monitoring of BUN levels is essential if a person has any pre-existing kidney disease of later stages, especially after observing few symptoms like:

  • Excessive fatigue
  • More frequent urination urge
  • Body itching
  • Edema which is persistent in arms, legs, and feet
  • Muscle cramping or twitching
  • Trouble Sleeping


BUN test

What is the procedure of a BUN test?

In this blood urea test, a healthcare professional takes the blood sample using a needle from the vein in the arm. After insertion of a needle, the blood sample is taken out in a vial or test tube. The process might take less than five minutes in total. This is a simple test without any pain except needle prick and with no bruising. There is no pre-test preparation required for this test.

You might have to avoid eating or drinking anything just a few hours before the test. Especially avoid intake of protein in foods to prevent any false test results. Besides this any specific requirement if any, will be shared by the physician who recommends the test. There is nothing scary in this test go for BUN Test.


What is the significance of BUN results?

Normal levels of BUN might vary in labs as per the reference range or age however an extremely high level of it indicates a hiding kidney disease inside your body. Sometimes abnormal BUN levels might not indicate any medical condition instead can also by certain excessive medication intake mainly painkillers, high protein-rich diets, burns, dehydration, and various other factors. These factors once removed can lead to normal BUN levels.

For a detailed analysis of the condition, a physician must be the right person to consult for this. Usually, 7 to 20 md/dL or 2.5 to 7.1 mmol/L is the preferable normal range for the BUN test. But it might vary from lab to lab. Infants exhibit low levels of BUN whereas with age the levels tend to increase mainly in old age and for children the range varies.


High BUN levels clearly reveal impaired kidney functioning most of the times. But in few cases, other factors might also affect and cause an elevation in levels. Such factors might include dehydration, congestive heart failure, urinary obstruction, gastrointestinal bleeding, shock, severe burns, protein-rich diets etc.

A physician might help to identify the actual cause of elevation in urea levels and by suggesting ways to minimize the impacts levels can be controlled. Also in case of real elevated BUN results few more tests including complete urinalysis and blood analysis can help the physician in identifying the real cause of kidney issue. Further receiving a correct treatment at the right time can help the person to reverse the kidney damage. The reversal is best possible in cases of early diagnosis of diseases.

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