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Normal BUN level in the blood

Blood test
Normal BUN level in the blood
Last update: 27/04/2020

What is the normal BUN level in the blood?

BUN normal ranges are age-related.


18 to 30 years old: 9 - 20 mg/dl
30 to 40 years old: 9 - 21 mg/dl
40 to 50 years old: 9 - 22 mg/dl
50 to 60 years old: 9 - 25 mg/dl
60 to 70 years old: 9 - 28 mg/dl
More than 70 years old: 9 - 32 mg/dl


1 to 17 years old: 5.5 - 20 mg/dL
Newborns: 3 - 14 mg/dL

In the International System of Units (SI), BUN in the blood is measured in mmol/L. The normal BUN level in the SI is:


18 to 30 years old: 3.21 - 7.14 mmol/l
30 to 40 years old : 3.21 - 7.5 mmol/l
40 to 50 years old: 3.21 - 7.85 mmol/l
50 to 60 years old: 3.21 - 8.92 mmol/l
60 to 70 years old: 3.21 - 10 mmol/l
More than 70 years old: 3.21 - 11.42 mmol/l L


1 to 17 years old: 1.96-7.14 mmol/l
Newborns: 1.07 - 5 mmol/l

Why normal levels can differ across different labs?

Each laboratory must establish its own normal ranges for BUN in the blood. These ranges depend on the makeup of the local population, the technologies used and the accuracy of the measurement. There may be also slight differences in the normal levels according to age, gender, race or ethnic origin, geographic region, diet, type of sample and other relevant status.

Your doctor will study the results along with your medical record, screenings, physical condition, symptoms and any other relevant information about your situation.

There are some circumstances to take into account about BUN normal ranges in the blood:

  • It important to know if the values measured are the BUN levels used in the US and other countries or instead the values measured are the total urea used in Europe and around the world. The relation is: Urea = BUN * 2.1428 or BUN= Urea * 0.4667.
  • Warning: In this page we talk about BUN levels. If your test is expressed in urea you must convert the values from urea to BUN or the information given will not be specific for your case.
  • Age is an important factor to normal ranges. Maximum values increase with the age and are higher in elderly people.

What is the role of BUN (Blood Urea Nitrogen)?

Urea is the final product of protein metabolism. Urea appears in the liver as a waste product and carry to the bloodstream. Later, it is filtered by the kidneys and excreted in urine. If the kidneys do not work efficiently, the urea will stay in the blood in high concentration and it can damage organs and tissues.

In the US and in a few other countries, urea concentration measures only the amount of urea nitrogen. It reflects only the nitrogen content of urea and it is referred as blood urea nitrogen (BUN). Around the world urea measurements usually considers the whole molecule. For that reason, urea is approximately twice the BUN values:

Urea = BUN * 2.1428

What is a BUN blood test used for?

Urea is a marker for kidneys and liver activity.

Urea level in the blood is directly related to nutrition, protein metabolism/catabolism and renal functionality.

A high level of BUN in the blood may be due to:

  • A decrease in the plasma volume due to dehydration or upper GI (gastrointestinal) bleeding
  • High protein catabolism (due to an excessive consumption of proteins, etc.)
  • Kidney disorders (kidney failure, nephropathies, etc.). If kidneys do not work properly urea remains in the bloodstream and its concentration in the blood will be abnormally higher.

A BUN level below the normal range may be a sign of a low-protein diet or a liver disorder (the liver is not doing a proper protein metabolism). Some disorders related to a low BUN level in the blood are pregnancy and acromegaly.

Where can I find more information about BUN level in the blood?

You can visit our pages about:

Which values are considered a normal BUN level in the blood?

The following values are considered to be normal values:

IMPORTANT: These levels are expressed in mg/dl. They are an example of a healthy man of about 45 years of age with no known disease, not taking any medication and with an appropriate intake of protein in the diet. The ranges can be different depending on the laboratory or on your personal circumstances.

9 mg/dl10 mg/dl11 mg/dl12 mg/dl13 mg/dl14 mg/dl15 mg/dl16 mg/dl
17 mg/dl18 mg/dl19 mg/dl20 mg/dl21 mg/dl22 mg/dl  
Medically reviewed by Javier Muga Bustamante Ph.D. on 27/04/2020


  • Concise Book of Medical Laboratory Technology: Methods and Interpretations. 2nd Edition. 2015. Ramnik Sood. ISBN: 978-93-5152-333-8. Pag. 468.
  • Thomas L. Urea and blood urea nitrogen (BUN). In:Thomas L, ed. Clinical laboratory diagnostics.Use and assessment of clinical laboratory results. Frankfurt/Main: TH-Books Verlagsgesellschaft, 1998:374-377.
  • Newman DJ, Price CP. Renal function and nitrogen metabolites. In: Burtis CA, Ashwood ER, eds. Tietz textbook of clinical chemistry. Philadelphia: WB Saunders Company, 1999;1239-1241.
  • Painter PC, Cope JY, Smith JL. Reference information for the clinical laboratory. In: Burtis CA, Ashwood ER, eds. Tietz textbook of clinical chemistry. Philadelphia:WB Saunders Company, 1999; 1838pp.
  • Lab Test: Blood Urea Nitrogen, BUN Level. Available on:

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