Kidney
Blood Urea Nitrogen (BUN)
LOINC 3094-0 · mg/dL
Ranges
Reference range: 7–20 mg/dL
What it is
Blood urea nitrogen (BUN) is the nitrogen carried in urea, the waste product left when protein is broken down, which the kidneys filter out.
Why it matters
It reflects kidney function, hydration and protein metabolism, and is read together with creatinine. Labs in the US and Mexico report BUN; most others report urea itself, which is about 2.14 times the BUN value, so compare a result with ones reported the same way.
What high values can mean
A higher value can reflect dehydration, a high-protein intake or reduced kidney function.
What low values can mean
A lower value can relate to low protein intake, overhydration or liver factors.
How to improve it
Good hydration and managing the underlying cause keep BUN in a normal range.
Food & lifestyle
Adequate fluids and balanced protein intake support a normal BUN; the broader kidney picture matters most.
Preparing for the test
A blood test, often with a metabolic panel; fasting is not specifically required — follow your lab.
When to talk to a doctor
A BUN outside the reference range is interpreted by a doctor with creatinine and eGFR to assess your kidneys.
Related markers
Sources
- MedlinePlus (NIH)
- Testing.com (AACC)
Content reviewed on October 26, 2026
Medical disclaimer
This content is for educational purposes only. It is not medical advice and does not diagnose, treat, or prevent any condition. Reference ranges vary between laboratories — always use the range printed on your report and discuss your results with a healthcare professional.
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