BUN (Blood Urea Nitrogen) is a blood test that measures bun (blood urea nitrogen) levels in the blood. Normal range: Urea (which Australian labs usually report rather than the US "BUN") is typically 3.0-8.0 mmol/L. It is a less specific kidney marker than creatinine because diet, hydration and bleeding all move it, but the urea-to-creatinine pattern is informative.. It is commonly used to helps evaluate kidney function and hydration status..
What is BUN (Blood Urea Nitrogen)?
A waste product filtered by the kidneys.
Why is it measured?
Helps evaluate kidney function and hydration status.
Normal Reference Range
Urea (which Australian labs usually report rather than the US "BUN") is typically 3.0-8.0 mmol/L. It is a less specific kidney marker than creatinine because diet, hydration and bleeding all move it, but the urea-to-creatinine pattern is informative.
Note: Reference ranges may vary between laboratories. Always consult your healthcare provider for interpretation.
What Causes High BUN?
High urea can mean reduced kidney function, but it is also raised by dehydration (the most common reversible cause), a high-protein diet, gastrointestinal bleeding (digested blood is absorbed protein), heart failure with reduced kidney perfusion, and catabolic states such as severe infection or steroid use. A high urea with a relatively normal creatinine typically signals dehydration rather than kidney disease.
What Causes Low BUN?
Low urea is generally harmless and reflects a low-protein diet, overhydration, or pregnancy (where blood volume expands and filtration increases). It can also occur in severe liver disease, since the liver makes urea — in that setting it is part of a wider picture of liver failure.
How Often Should BUN Be Tested?
Urea is part of the routine UEC (urea, electrolytes, creatinine) panel and is measured whenever kidney function, hydration or electrolytes are assessed. It is monitored in chronic kidney disease, heart failure, acute illness and during hospital admissions.
Related Blood Markers
Urea is interpreted with creatinine and eGFR (the urea:creatinine ratio distinguishes dehydration from kidney disease) and with the electrolytes sodium and potassium.
Key Facts
- •Category: Vital Organ Functions
- •Unit of Measurement: mmol/L
- •Test Code: BUN
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