What is BUN?
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.
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.
Why might BUN be low?
Low BUN may be associated with a low-protein diet, over-hydration, liver disease (reduced urea production), or pregnancy.
This information is educational. A single out-of-range result is rarely the whole picture — a healthcare professional can interpret your numbers alongside your overall health and history.
Context questions that matter
- →Was this result slightly or clearly outside the reference range?
- →Were related markers also high or low?
- →Is this new compared with previous tests?
- →Could recent illness, exercise, fasting, alcohol, supplements, or medication affect it?
- →Do you have symptoms that should be discussed with a clinician?
Markers often reviewed together with BUN
Clinicians rarely look at one number in isolation. These markers usually accompany BUN on a kidney function panel and help put the result in context.
Questions to ask your doctor
- →Should we compare this with creatinine, eGFR, urea and electrolytes?
- →Could hydration, age, muscle mass, or medication affect this low BUN result?
- →Is this result new, or part of a trend across my previous tests?
Don't guess from one flagged result.
Start with the most relevant panel and see how your markers fit together in plain English.
Frequently asked questions
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.
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.
Should BUN be read with eGFR or creatinine?
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Kidney markers are usually interpreted together. Creatinine, eGFR (creatinine-based or cystatin-C-based), urea (BUN), electrolytes and urine markers such as the albumin/creatinine ratio give a fuller picture than any single value.
Can hydration affect kidney-related results?
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Hydration, recent illness, muscle mass, age and some medicines can affect kidney-related markers. A single value is interpreted with these factors and with the trend across previous tests — your doctor can put the number in context using your full report.