What is the difference between BUN and Urea?
In clinical laboratory reports, kidney function is often assessed by measuring nitrogenous waste. Blood Urea Nitrogen (BUN) measures the amount of nitrogen in the blood that comes from urea, while Urea refers to the entire urea molecule.
The transition between these two values is purely mathematical, based on the molecular weight of the components. Urea has a molecular weight of 60 Da, while the two nitrogen atoms within it account for 28 Da. This creates a constant ratio used worldwide in medical diagnostics.
Why Convert BUN to Urea?
Standardization is the primary reason for conversion. While the United States, Austria, and Germany typically use BUN (reported in mg/dL), most other countries report the full Urea molecule (often in mmol/L or mg/dL). Converting between them allows for a universal comparison of a patient's renal health, particularly when calculating the BUN/Creatinine ratio to distinguish between pre-renal and intrinsic renal failure.
Formula:
The Conversion Factor:
- To get Urea: BUN × 2.14
- To get BUN: Urea / 2.14