Blood urea nitrogen

Blood urea nitrogen
Diagnostics

MeSH D001806
LOINC 6299-2, 59570-2, 12961-9, 12963-5, 12962-7

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 to 20 mg of urea nitrogen per 100 ml (6–20 mg/dL) of blood. Individual laboratories may have different reference ranges, and this is because the procedure may vary.[1][2]

Interpretation

BUN is an indication of renal health. Normal ranges 8-20 mmol/L.

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.

The main causes of a decrease in BUN are: severe liver disease, anabolic state, syndrome of inappropriate antidiuretic hormone.[3]

Reference ranges for blood tests, comparing urea (yellow at right) to other blood constituents.

Units

BUN (urea-N) is mg/dL in the United States, Mexico, 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, multiply by 0.357 (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 = 1 for conversions in mmol (1 mole N2 = 2 moles N per mole of urea):

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