Blood urea nitrogen

Blood urea nitrogen
Diagnostics
Urea
MeSH	D001806
LOINC	6299-2, 59570-2, 12961-9, 12963-5, 12962-7

The blood urea nitrogen (BUN, pronounced "B-U-N") test is a measure of the amount of nitrogen in the blood in the form of urea, and a measurement of renal function. Urea is a by- product from metabolism of proteins by the liver and is removed from the blood by the kidneys.

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.^[1]^[2]

1 Interpretation
2 Units
3 See also
4 References
5 External links

Interpretation

Units

BUN (urea-N) is reported as mg/dL in the United States, 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, divide by 2.8 (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 = 2 for conversions in mmol (2 moles N per mole of urea):

BUN [mmol/L]= 2x urea [mmol/L]

References

^ 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.