Blood urea nitrogen
|Blood urea nitrogen|
|LOINC||6299-2, 59570-2, 12961-9, 12963-5, 12962-7|
The liver produces urea in the urea cycle as a waste product of the digestion of protein. Normal human adult blood should contain between 7 to 21 mg of urea nitrogen per 100 ml (7–21 mg/dL) of blood. Individual laboratories may have different reference ranges, and this is because the procedure may vary.[dead link]
BUN is an indication of renal health. Normal ranges 8-20 mmol/L. If Glomerular Filtration Rate (GFR) and blood volume decrease (hypovolemia) then BUN will increase.Other factors responsible for its increment are fever, increased catabolism, high protein diet and gastrointestinal bleeding.
BUN (urea-N) is g/dL in the United States, Mexico, Italy, Austria, Germany. Elsewhere, the concentration of urea is reported as mmol/L, generally depending on the lab.
To convert from mg/dL of blood urea nitrogen to mmol/L of urea, multiply by 0.357 (each molecule of urea having 2 nitrogens, each of molar mass 14g/mol)
- Urea [mmol/L] = BUN [mg/dL of nitrogen] x 10 [dL/L] / 14x2 [mg N/mmol urea]
convert BUN to urea in mg/dL by using following formula:
- Urea [mg/dL]= BUN [mg/dL] * 2.14
(conversion factor derived by: MW of urea = 60, MW of urea nitrogen = 14x2 => 60/28 = 2.14)
factor = 1 for conversions in mmol (1 mole N2 = 2 moles N per mole of urea):
- BUN [mmol/L]= urea [mmol/L]
See also 
- Last page of Deepak A. Rao; Le, Tao; Bhushan, Vikas (2007). First Aid for the USMLE Step 1 2008 (First Aid for the Usmle Step 1). McGraw-Hill Medical. ISBN 0-07-149868-0.
- Normal Reference Range Table from The University of Texas Southwestern Medical Center at Dallas. Used in Interactive Case Study Companion to PATHOLOGIC BASIS of DISEASE.