Blood urea nitrogen: Difference between revisions

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

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Blood urea nitrogen (BUN) is a medical test that measures the amount of urea nitrogen found in blood. The liver produces urea in the urea cycle as a waste product of the digestion of protein. Normal human adult blood should contain 6 to 20 mg/dL (2.1 to 7.1 mmol/L) of urea nitrogen.^[1] Individual laboratories will have different reference ranges as the assay used can vary between laboratories.^[2]^[3]^[4] The test is used to detect renal problems. It is not considered as reliable as Creatinine or Bun/Creatitine ratio blood studies.^[1]

Interpretation

BUN is an indication of renal (kidney) health. The normal range is 2.1–7.1 mmol/L or 6–20 mg/dL.^[1]

The main causes of an increase in BUN are: high protein diet, decrease in glomerular filtration rate (GFR) (suggestive of kidney failure), decrease in blood volume (hypovolemia), congestive heart failure, gastrointestinal hemorrhage,^[5] fever, rapid cell destruction from infections, athletic activity, excessive muscle breakdown, and increased catabolism.^[1]

Hypothyroidism can cause both decreased GFR and hypovolemia, but BUN-to-creatinine ratio has been found to be lowered in hypothyroidism and raised in hyperthyroidism.

The main causes of a decrease in BUN are severe liver disease, anabolic state, and syndrome of inappropriate antidiuretic hormone.^[5]

Another rare cause of a decreased BUN is ornithine transcarbamylase deficiency, which is a genetic disorder inherited in an X-linked recessive pattern. OTC deficiency is also accompanied by hyperammonemia and high orotic acid levels.

Units

BUN (urea-N) is mg/dL in the United States, Mexico, Italy, Austria, and Germany. Elsewhere, the concentration of urea is reported in SI unit as mmol/L, which is generally depending on the lab.

$BUN_{mg/dL}$ represents the mass of nitrogen within urea/volume, not the mass of whole urea. Each molecule of urea has two nitrogen atoms, each of molar mass 14g/mol. To convert from mg/dL of blood urea nitrogen to mmol/L of urea:

$Urea_{mmol/L}=BUN_{mmol/L}=BUN_{mg/dL}*{\frac {10_{dL/L}}{14*2}}=BUN_{mg/dL}*0.3571$

Note that molar concentrations of urea and urea nitrogen are equal, because both nitrogen gas and urea has two nitrogen atoms.

Convert BUN to urea in mg/dL by using following formula:

$Urea_{mg/dL}=BUN_{mg/dL}*{\frac {60}{14*2}}=BUN_{mg/dL}*2.14$

Where 60 represents MW of urea and 14*2 MW of urea nitrogen.

References

^ ^a ^b ^c ^d Lewis, Sharon Mantik; Dirksen, Shannon Ruff; Heitkemper, Margaret M.; Bucher, Linda; Harding, Mariann. Medical-surgical nursing : assessment and management of clinical problems (9th ed.). St. Louis, Missouri. ISBN 978-0-323-10089-2. OCLC 228373703.
^ Tao Le; Vikas Bhushan; Deepak Rao (2007). First Aid for the USMLE Step 1 2008. New York: McGraw-Hill Medical. Last page. ISBN 978-0-07-149868-5.
^ "Normal Lab Results". Marshal University School of Medicine. Archived from the original on December 16, 2014.
^ "Blood urea nitrogen (BUN) test - Mayo Clinic". www.mayoclinic.org. Retrieved 2019-05-13.
^ ^a ^b Longo; et al. Harrison's Principles of Internal Medicine (18th ed.). p. 611.^{[full citation needed]}

External links

[:1-1] Lewis, Sharon Mantik; Dirksen, Shannon Ruff; Heitkemper, Margaret M.; Bucher, Linda; Harding, Mariann. Medical-surgical nursing : assessment and management of clinical problems (9th ed.). St. Louis, Missouri. ISBN 978-0-323-10089-2. OCLC 228373703.

[firstaid-2] Tao Le; Vikas Bhushan; Deepak Rao (2007). First Aid for the USMLE Step 1 2008. New York: McGraw-Hill Medical. Last page. ISBN 978-0-07-149868-5.

[Marshall-3] "Normal Lab Results". Marshal University School of Medicine. Archived from the original on December 16, 2014.

[4] "Blood urea nitrogen (BUN) test - Mayo Clinic". www.mayoclinic.org. Retrieved 2019-05-13.

[:0-5] Longo; et al. Harrison's Principles of Internal Medicine (18th ed.). p. 611.^{[full citation needed]}

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 ==Units==
-BUN (urea-N) is mg/dL in the United States, Mexico, Italy, Austria, and Germany. Elsewhere, the concentration of urea is reported as mmol/L, generally depending on the lab.
+BUN (urea-N) is mg/dL in the United States, Mexico, Italy, Austria, and Germany. Elsewhere, the concentration of urea is reported in SI unit as mmol/L, which is generally depending on the lab.
+<math chem>BUN_{mg/dL}</math> represents the mass of nitrogen within urea/volume, not the mass of whole urea. Each molecule of urea has two nitrogen atoms, each of molar mass 14g/mol. To convert from mg/dL of blood urea nitrogen to mmol/L of urea:
-BUN (urea-N) SI unit is mmol/L
-BUN [mmol/L] = BUN [mg/dL] * 0.3571
+<math chem>Urea_{mmol/L} = BUN_{mmol/L} = BUN_{mg/dL} * \frac{10_{dL/L}}{14*2} = BUN_{mg/dL} * 0.3571</math>
+Note that molar concentrations of urea and urea nitrogen are equal, because both nitrogen gas and urea has two nitrogen atoms.
-To convert from mg/dL of blood urea nitrogen to mmol/L of urea, multiply by 0.357 (each molecule of urea having two nitrogens, each of molar mass 14g/mol) (BUN is the mass of nitrogen within urea/volume, not the mass of urea)
-::Urea [mmol/L] = BUN [mg/dL of [[nitrogen]]] x 10 [dL/L] / 14x2  [mg N/mmol urea] (the mass of nitrogen within urea is used)
-convert BUN to urea in mg/dL by using following formula:
+Convert BUN to urea in mg/dL by using following formula:
-::Urea [mg/dL]= BUN [mg/dL] * 2.14
+<math chem>Urea_{mg/dL} = BUN_{mg/dL} * \frac{60}{14*2} = BUN_{mg/dL} * 2.14 </math>
-(conversion factor derived by: MW of urea = 60, MW of urea nitrogen = 14x2 => 60/28 = 2.14)
+Where 60 represents MW of urea and 14*2 MW of urea nitrogen.
-factor = 1 for conversions in mmol (1 mole N<sub>2</sub> = 2 moles N per mole of urea):
-::BUN [mmol/L]= urea [mmol/L]
 ==See also==