Blood urea nitrogen
| Blood urea nitrogen | |
|---|---|
| Medical diagnostics | |
 Urea | |
| MeSH | D001806 |
| LOINC | 6299-2, 59570-2, 12961-9, 12963-5, 12962-7 |
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 between 6 and 20 mg of urea nitrogen per 100 ml (6–20 mg/dL) of blood. Individual laboratories will have different reference ranges as the assay used can vary between laboratories.[1][2]
Contents
1 Interpretation
2 Units
3 See also
4 References
5 External links
Interpretation
BUN is an indication of renal (kidney) health. The normal range is 1.8–7.1 mmol/L or 6–20 mg/dL.
The main causes of an increase in BUN are: high protein diet, decrease in glomerular filtration rate (GFR) (suggestive of renal failure) and in blood volume (hypovolemia), congestive heart failure, gastrointestinal hemorrhage,[3]fever, and increased catabolism. 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.[3]
Reference ranges for blood tests, comparing urea (yellow at right) to other blood constituents
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 as mmol/L, generally depending on the lab.
BUN (urea-N) SI unit is mmol/L
BUN [mmol/L] = BUN [mg/dL] * 0.3571
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:
- 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
- Kt/V
- Urea reduction ratio
- Urine urea nitrogen
- Standardized Kt/V
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..mw-parser-output cite.citation{font-style:inherit}.mw-parser-output q{quotes:"""""""'""'"}.mw-parser-output code.cs1-code{color:inherit;background:inherit;border:inherit;padding:inherit}.mw-parser-output .cs1-lock-free a{background:url("//upload.wikimedia.org/wikipedia/commons/thumb/6/65/Lock-green.svg/9px-Lock-green.svg.png")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-lock-limited a,.mw-parser-output .cs1-lock-registration a{background:url("//upload.wikimedia.org/wikipedia/commons/thumb/d/d6/Lock-gray-alt-2.svg/9px-Lock-gray-alt-2.svg.png")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-lock-subscription a{background:url("//upload.wikimedia.org/wikipedia/commons/thumb/a/aa/Lock-red-alt-2.svg/9px-Lock-red-alt-2.svg.png")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registration{color:#555}.mw-parser-output .cs1-subscription span,.mw-parser-output .cs1-registration span{border-bottom:1px dotted;cursor:help}.mw-parser-output .cs1-hidden-error{display:none;font-size:100%}.mw-parser-output .cs1-visible-error{font-size:100%}.mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registration,.mw-parser-output .cs1-format{font-size:95%}.mw-parser-output .cs1-kern-left,.mw-parser-output .cs1-kern-wl-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right,.mw-parser-output .cs1-kern-wl-right{padding-right:0.2em}
^ Normal Lab Results Archived December 16, 2014, at the Wayback Machine. from Marshal University School of Medicine
^ ab Longo et al., Harrison's Principles of Internal Medicine, 18th ed., p.611
