Blood urea nitrogen (BUN) is a medical test that measures the amount of ureanitrogen found in blood. The liver produces urea in the urea cycle as a waste product of the digestionofprotein. Normal human adult blood should contain 7 to 18 mg/dL (0.388 to 1 mmol/L) of urea nitrogen.[1] Individual laboratories may have different reference ranges, as they may use different assays.[2][3][4] The test is used to detect kidney problems. It is not considered as reliable as creatinineorBUN-to-creatinine ratio blood studies.[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.
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.
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.
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:
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:
Where 60 represents MW of urea and 14*2 MW of urea nitrogen.
