Urea nitrogen (BUN) Unit Conversion

Measurements of urea nitrogen are used in the diagnosis and treatment of certain renal and metabolic disorders.

Urea nitrogen makes up approximately 75% of the total non-protein nitrogen (NPN) fraction of the blood. BUN is the major end product of protein nitrogen metabolism. It is synthesized by the urea cycle in the liver from ammonia which is produced by amino acid deamination. Urea is excreted mostly by the kidneys but minimal amounts are also excreted in sweat and degraded in the intestines by bacterial action.

Determination of blood urea nitrogen is the most widely used screening test for renal function. When used in conjunction with serum creatinine determinations it can aid in the differential diagnosis of the three types of azotemia: prerenal, renal, and postrenal.

Elevations in blood urea nitrogen concentration are seen in inadequate renal perfusion, shock, diminished blood volume (prerenal causes), chronic nephritis, nephrosclerosis, tubular necrosis, glomerular-nephritis (renal causes), and urinary tract obstruction (postrenal causes). Transient elevations may also be seen during periods of high protein intake. Unpredictable levels occur with liver diseases.

Convert BUN mg/dL to mmol/L of urea by using following formula: ¹

BUN [mg/dL] x 0.357 = Urea [mmol/L]

Convert BUN to urea in mg/dL by using following formula: ²

BUN [mg/dL] x 2.14 = Urea [mg/dL]

Convert Urea to BUN in mg/dL by using following formula: ³

Urea [mg/dL] x 0.467 = BUN [mg/dL]

Convert BUN to Urea in mmol/L by using following formula: ⁴

BUN [mmol/L] x 1 = Urea [mmol/L]

Convert Urea to BUN in mmol/L by using following formula: ⁴

Urea [mmol/L] x 1 = BUN [mmol/L]

1) 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) (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)

2) Conversion factor derived by: 60/28 = 2.14 (MW of Urea = 60, MW of urea nitrogen = 28 (14x2)

3) Conversion factor derived by: 28/60= 0.467 (MW of urea nitrogen = 28 (14x2), MW of Urea = 60

4) Factor = 1 for conversions in mmol (1 mole N2 = 2 moles N per mole of urea): BUN [mmol/L] = urea [mmol/L]

REFERENCE INTERVALS
Serum/plasma (reference range according Tietz)
Adult (18‐60 years)   2.14‐7.14 mmol/L   (6‐20 mg/dL)
Adult (60‐90 years)   2.86‐8.21 mmol/L   (8‐23 mg/dL)
Infant (< 1 year)     1.43‐6.78 mmol/L   (4‐19 mg/dL)
Infant/child          1.79‐6.43 mmol/L   (5‐18 mg/dL)