Blood and lab tests
What Does BUN Mean on a Blood Test?
BUN · say it: B-U-NAlso written: blood urea nitrogen, urea, serum urea, urea nitrogen
Short answer
BUN, or blood urea nitrogen, measures a waste product from protein breakdown that the kidneys clear from the blood.
What it means
BUN stands for blood urea nitrogen. When the body breaks down protein, the liver turns the leftover nitrogen into a waste product called urea. Urea travels in the blood to the kidneys, which filter it out into the urine. BUN measures how much of that urea is in the blood.
BUN is part of the basic and comprehensive metabolic panels and of kidney function tests. Doctors read it alongside creatinine and eGFR to judge how well the kidneys are clearing waste. BUN is affected by more than the kidneys, though: dehydration, a high-protein diet, bleeding in the stomach or gut, and steroid medicines can raise it, while liver disease and low protein intake can lower it.
In the UK and many other countries, the same test is reported as "urea" in different units. The idea is the same, but the numbers are not directly comparable, so it matters which name your report uses.
Where you may see it
- Basic and comprehensive metabolic panels (BMP and CMP)
- Kidney function results next to creatinine and eGFR
- Hospital blood tests, listed as "Urea" on UK reports
📄 How it looks on a report
BUN 28 mg/dL H
🙅 What it does not mean
- A high BUN does not by itself mean kidney disease. Not drinking enough fluid is a very common reason.
- A low BUN is often not a concern. It can reflect a low-protein diet, pregnancy or plenty of fluids.
- BUN and creatinine are not the same test. Creatinine is usually a steadier guide to how well the kidneys filter.
🗒️ Questions to ask your doctor
🧾 Reports where you will see “BUN”
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💊 Medicines whose labels mention “BUN”
Plain-English explanations of each medicine, from its official FDA label.
- Bumetanide
a loop diuretic, which is a type of water pill
- Divalproex Sodium
An anti-epileptic (anti-seizure) drug of the valproate type. The label also uses it to treat manic episodes of bipolar disorder and to prevent migraine headaches.
- Ergocalciferol
a synthetic vitamin D medicine that regulates calcium (FDA class: Provitamin D2 Compound)
- Furosemide
A loop diuretic, a type of medicine that helps the body get rid of extra fluid through urine
🔗 Read more from trusted sources
- “BUN” on MedlinePlus ↗
US National Library of Medicine
- MedlinePlus lab test guides ↗
US National Library of Medicine
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General information about a medical word, not advice about your own results. Ask the clinician who ordered the test what it means for you.