BUN (Blood Urea Nitrogen)
BUN is a waste product of protein metabolism, removed from the blood by the kidneys. Like creatinine, BUN reflects kidney filtration — but it is also influenced by hydration, protein intake, and gastrointestinal bleeding, making it less specific than creatinine alone.
Normal Range
7–20 mg/dL
Reference ranges may vary slightly between laboratories. Always interpret your result in context with your doctor.
Why is BUN measured?
BUN is part of the basic metabolic panel and is used to evaluate kidney function, hydration status, and certain causes of acute illness. The BUN/creatinine ratio helps distinguish dehydration from intrinsic kidney disease.
High BUN means…
High BUN can indicate dehydration, kidney disease, high-protein diet, gastrointestinal bleeding, or heart failure. A BUN/creatinine ratio above 20 typically suggests dehydration or GI bleed; a ratio below 10 may suggest liver disease or malnutrition.
Low BUN means…
Low BUN is uncommon and may reflect very low protein intake, severe liver disease (reduced urea production), or excessive fluid intake.
Symptoms associated with abnormal BUN
When BUN is high:
- Often no symptoms; depends on cause
- Fatigue, confusion (uraemia)
- Dehydration signs
- Decreased urine output
When BUN is low:
- Usually asymptomatic
How to improve your BUN
- Always interpret BUN alongside creatinine — the ratio is more informative.
- If BUN is high but creatinine is normal, hydration is often the answer.
- Persistent high BUN with high creatinine signals kidney disease — discuss with your doctor.
Frequently asked questions about BUN
What is the BUN/creatinine ratio?
The BUN/creatinine ratio (normal 10–20) helps locate the cause of kidney dysfunction. Above 20 suggests dehydration or GI bleed (pre-renal). 10–20 suggests intrinsic kidney disease. Below 10 suggests liver disease or malnutrition.
Does high-protein diet raise BUN?
Yes — modestly. A high-protein diet (such as keto or carnivore) can push BUN to 25–35 mg/dL without indicating kidney problems, provided creatinine and eGFR remain normal.
Medical Sources
This page is for informational purposes only and does not constitute medical advice. Always consult a qualified healthcare provider about your individual results.