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Low BUN level in the blood

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

What is a low BUN level in the blood called?

  • Hypoazotemia

What is the normal BUN level in the blood?

If you need to know which are the BUN reference ranges or you require more information about the role of BUN in the blood, you can visit normal BUN level in the blood

What does a low BUN level in the blood mean?

Hypoazotemia (low values of BUN in the blood) is not common. It can be a consequence of malnutrition with a low-protein diet and high water intake.

Hypoazotemia can be a sign of liver disorders, but the BUN it is not used as a diagnose test for the liver because there are other parameters which give better information about liver status.

BUN values are usually given in mg/dl but sometimes you can see those values in mmol/l following the International System of Units (SI). In case your values are in mmol/l you can convert them using this web

Warning: In Europe and other countries, the values measured are the total urea instead of BUN (Blood urea nitrogen). The formula to convert from BUN to urea is BUN= Urea * 0.4667. You can convert them using this tool.

  • Mild hypoazotemia (4.5 - 9 mg/dl in adults):

    Mild hypoazotemia is not usually a matter of concern.

    The main reason is a low-protein diet or over hydration (high intake of water and liquids). It is common a low value of BUN in vegetarians due to the low protein intake.

  • Marked hypoazotemia (<4.5 mg/dl in adults):

    Marked hypoazotemia can be a sign of a liver disorder.

    However, when there is a liver disorder, it is better to study other blood test parameters.

Which factors can reduce the BUN level in the blood?

There are some circumstances than can reduce your BUN level in the blood:

  • Low-protein diet
  • Pregnancy (second and third trimester)
  • Over hydration
  • Hemodialysis
  • Malabsorption
  • Tobacco

Which diseases can reduce your BUN level in the blood?

Lower than normal level of BUN in the blood can be due to:

  • Pancreatic insufficiency
  • Eclampsia
  • Cystic fibrosis

What can I do to increase BUN level in the blood?

If the BUN level in the blood is a bit high, you can consider the following tips:

  • Increase your protein intake. Meat, fish, milk and eggs are foods with a high protein content. If you are vegetarian, nuts (almonds, walnuts, hazelnuts, peanuts, etc.) and soya are an alternative source of proteins.
  • Reduce the water and liquid intake. A high water intake may be detrimental.

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

You can visit our pages about:

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

The following values are considered to be below the normal range:

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.

Mild hypoazotemia
8.9 mg/dl8.8 mg/dl8.7 mg/dl8.6 mg/dl8.5 mg/dl8.4 mg/dl8.3 mg/dl8.2 mg/dl
8.1 mg/dl8 mg/dl7.9 mg/dl7.8 mg/dl7.7 mg/dl7.6 mg/dl7.5 mg/dl7.4 mg/dl
7.3 mg/dl7.2 mg/dl7.1 mg/dl7 mg/dl6.9 mg/dl6.8 mg/dl6.7 mg/dl6.6 mg/dl
6.5 mg/dl6.4 mg/dl6.3 mg/dl6.2 mg/dl6.1 mg/dl6 mg/dl5.9 mg/dl5.8 mg/dl
5.7 mg/dl5.6 mg/dl5.5 mg/dl5.4 mg/dl5.3 mg/dl5.2 mg/dl5.1 mg/dl5 mg/dl
4.9 mg/dl4.8 mg/dl4.7 mg/dl4.6 mg/dl4.5 mg/dl   
Marked hypoazotemia
4.4 mg/dl4.3 mg/dl4.2 mg/dl4.1 mg/dl4 mg/dl3.9 mg/dl3.8 mg/dl3.7 mg/dl
3.6 mg/dl3.5 mg/dl3.4 mg/dl3.3 mg/dl3.2 mg/dl3.1 mg/dl3 mg/dl2.9 mg/dl
2.8 mg/dl2.7 mg/dl2.6 mg/dl2.5 mg/dl2.4 mg/dl2.3 mg/dl2.2 mg/dl2.1 mg/dl
2 mg/dl1.9 mg/dl1.8 mg/dl1.7 mg/dl1.6 mg/dl1.5 mg/dl1.4 mg/dl1.3 mg/dl
1.2 mg/dl1.1 mg/dl1 mg/dl0.9 mg/dl0.8 mg/dl0.7 mg/dl0.6 mg/dl0.5 mg/dl
0.4 mg/dl0.3 mg/dl0.2 mg/dl0.1 mg/dl0 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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