BUN (clinical analyzes)




BUN indicates the concentration of non-protein nitrogen present in the blood.

Nitrogen is distinguished in protein and non-protein nitrogen on the basis of the use that the organism makes of it: protein nitrogen is used within the structure of the molecules that form proteins (amino acids), the non-protein one is instead , present in the waste substances of the organism.

BUN mainly reflects the content in the blood of a substance, urea, present in a higher concentration than other nitrogenous substances. Urea production occurs mainly in the liver and is subsequently eliminated by the kidneys in the urine, while a small amount is reabsorbed.

The azotemia test is recommended by the doctor in order to evaluate the correct functioning of the kidneys.

BUN levels that are too high or too low can also be caused by other factors such as excessive exercise or a diet that is too high in protein. For this reason, the azotemia dosage is often associated with another test, which consists in verifying the amount of creatinine present in the blood, much more precise in diagnosing a malfunction or a disease of the kidneys because it is not influenced by external conditions such as "supply.

The test

The test

The blood urea nitrogen test is performed by simply drawing blood by inserting a needle into a vein in the arm. It requires to be fasting from the night before and not to carry out physical activities of particular intensity in the previous days because the test results could be altered.

The test can be ordered as part of a normal control (routine control), but becomes indispensable if symptoms of renal failure or hepatitis occur, such as:

  • frequent urge to urinate
  • need to drink often
  • abnormalities in urine (e.g. darker colored, bloody, or foamy urine)
  • joint pain
  • bone pain
  • backache
  • frequent muscle cramps
  • feeling of tired legs
  • tiredness and exhaustion
  • problems while sleeping (difficulty falling asleep or returning to sleep, awakening at night, sleepiness during the day)
  • high pressure (hypertension)
  • decrease or disappearance of appetite
  • swelling (mainly located in the extremities, such as hands and feet)
  • unmotivated itching

The test, combined with that of creatinine, is also used to monitor the functioning of the kidneys in patients suffering from kidney failure or who are on dialysis.



Normal BUN levels may vary depending on the values ​​(range) of reference adopted by each analysis laboratory. In adults, they range from 22 to 46 milligrams per deciliter (mg / dL). Some laboratories, however, use different methods of analysis by referring to the "urea nitrogen index (blood urea nitrogen o BUN in English); in this case the normal azotemia values ​​are between 10.3 and 21.4 mg / dl. Usually, however, in the results of the analyzes, in addition to showing the azotemia value found, the minimum and maximum levels of normality are also indicated.

A high urea nitrogen value is not necessarily a sign of reduced kidney function. It may be a sign of kidney failure, but there are many other diseases in which it is present, such as:

  • decreased blood flow to the kidneys due to heart failure, bleeding or burns
  • recent acute myocardial infarction (heart muscle tissue)
  • bleeding from the gastrointestinal tract
  • problems causing urinary flow difficulties (stones or enlarged prostate)
  • dehydration (occurs when the amount of water lost through sweating, breathing, kidney function is greater than that introduced with liquids and food. It is caused by vomiting, diarrhea, poor fluid intake, heart failure, sweating, intense physical activity)
  • diet too high in protein
  • pregnancy
  • fast

Lower than normal azotemia values ​​could instead be linked to:

  • diet too low in protein
  • overhydration
  • liver failure
  • presence of kidney damage

It is important to underline that, in any case, the reading and interpretation of the results must be performed by the general practitioner and possibly by a specialist.



Niguarda Hospital. BUN and creatinine to assess kidney health

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