Blood urea nitrogen

Blood urea nitrogen
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

The main causes of a decrease in BUN are malnutrition (low-protein diet), 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 is usually reported in mg/dL in some countries (e.g. United States, Mexico, Italy, Austria, and Germany). Elsewhere, the concentration of urea is reported in SI units as mmol/L.

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

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

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:

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

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

See also

• Kt/V
• Standardized Kt/V
• Urea reduction ratio
• Urine urea nitrogen

References