Blood Urea Nitrogen
- Sample Type
- Serum
- Fasting
- No
- Unit
- mg/dL
Function
Blood Urea Nitrogen (BUN) measures the amount of urea nitrogen in the blood. Urea is a waste product created in the liver when the body breaks down proteins. It is then transported through the blood to the kidneys, which filter it out of the blood and into the urine. The BUN test is a fundamental indicator of how well the kidneys and liver are functioning.
Why it is Ordered
The BUN test is frequently ordered as part of a Basic or Comprehensive Metabolic Panel (BMP/CMP) during routine check-ups. It is also used to monitor patients with chronic conditions like kidney disease, heart failure, or diabetes. Doctors use it to evaluate the effectiveness of dialysis treatment or to help diagnose the cause of symptoms like fatigue, swelling (edema), or changes in urination.
Associated Conditions
- Kidney Dysfunction: High levels often indicate reduced glomerular filtration rate (GFR).
- Dehydration: Dehydration leads to higher concentration of urea in the blood.
- Congestive Heart Failure: Reduced blood flow to the kidneys can elevate BUN.
- Gastrointestinal Bleed: Digestion of blood proteins can significantly spike BUN levels.
- Liver Disease: Very low BUN levels may indicate impaired liver function (as the liver cannot produce urea).
Check Your Result
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Enter your lab result to see where you stand compared to the standard reference range.
Why Context Matters
BUN levels are highly sensitive to non-renal factors. A high-protein diet (like Keto) or the use of certain medications (steroids, antibiotics) can artificially inflate BUN levels even when kidney function is normal. Conversely, overhydration can dilute the blood and lower the BUN. Because it is influenced by hydration and diet, BUN is usually interpreted alongside Creatinine (the BUN/Creatinine ratio) for a more accurate diagnosis.
Lab ranges are statistical averages, not biological laws. "Normal" for a 20-year-old male isn't normal for a 60-year-old female.
Clinical References
Source-of-truth databases and clinical guidelines for Blood Urea Nitrogen:
Official Sources
Research & Guidelines
- PubMed: Blood Urea Nitrogen Clinical GuidelinesNCBI / PubMed
Related Indicators
Medically Reviewed by Dr. Binoy Babu, MBBS
Board Certified Doctor • 10+ Years Clinical Experience
Dr. Babu is a practicing physician dedicated to empowering patients with clear, actionable medical information. He founded 2opi to bridge the gap between complex lab reports and patient understanding, ensuring everyone has access to a reliable second opinion.
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