What this marker measures
The BUN-to-creatinine ratio helps distinguish kidney causes (ratio normal) from non-kidney causes (ratio high, suggesting dehydration or GI bleed). A ratio above 20:1 often points to a pre-renal cause.
High or low: what it can mean
High BUN
A high BUN can reflect kidney stress, dehydration, a high-protein diet, gastrointestinal bleeding, or increased protein catabolism. It is most informative when evaluated alongside creatinine.
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Low BUN
Low BUN may be associated with a low-protein diet, over-hydration, liver disease (reduced urea production), or pregnancy.
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Frequently asked questions
What is BUN?
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BUN measures urea nitrogen in the blood, a waste product from protein metabolism. The kidneys filter urea from the blood; elevated BUN can indicate reduced kidney filtering or increased protein breakdown.
What does BUN measure?
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The BUN-to-creatinine ratio helps distinguish kidney causes (ratio normal) from non-kidney causes (ratio high, suggesting dehydration or GI bleed). A ratio above 20:1 often points to a pre-renal cause.
What does high BUN mean?
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A high BUN can reflect kidney stress, dehydration, a high-protein diet, gastrointestinal bleeding, or increased protein catabolism. It is most informative when evaluated alongside creatinine.
What does low BUN mean?
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Low BUN may be associated with a low-protein diet, over-hydration, liver disease (reduced urea production), or pregnancy.
Related biomarkers
Editorial note
LabTestly explains lab markers using plain-English educational content. Reference ranges may vary by laboratory and should be interpreted with a clinician.
Educational content · Editorially reviewed for clarity · Last updated
Common sources used for lab-test education
Not medical advice
This page is for general understanding only and does not replace medical advice from your clinician. Reference ranges can vary by laboratory, age, sex, pregnancy status, medications, and clinical context.