BUN blood test
Blood urea nitrogen
In short
A typical adult BUN result is 6 to 21 mg/dL for women and 8 to 24 mg/dL for men. A mildly high BUN often comes from low fluids or a high-protein diet. Doctors read it with creatinine to see whether the kidneys are involved. Always read your result against the range printed on your own report.
A waste product made when the body breaks down protein.
Your liver turns leftover protein into urea, and your kidneys pass it out in urine. BUN measures the nitrogen part of that urea. It rises and falls with kidney function, but also with fluids and diet.
Is my BUN high or low?
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Typical range
| For | Range | Unit |
|---|---|---|
| Female | 6–21 | mg/dL |
| Male | 8–24 | mg/dL |
| Female | 2.1–7.5 | mmol/L |
| Male | 2.9–8.6 | mmol/L |
Typical ranges for adults. Labs differ a little, so the range printed next to your result is the one to go by.
If your BUN is high
A mildly high BUN often comes from low fluids or a high-protein diet. Doctors read it with creatinine to see whether the kidneys are involved.
Common reasons
- Not drinking enough, or losing fluid through sweat, vomiting or diarrhea
- A high-protein diet or protein supplements
- Steroid medicines, or a recent illness, injury or surgery
- Older age, as kidney filtering slowly falls
- Kidneys filtering less, often with diabetes or high blood pressure
- Less often: bleeding in the stomach or gut, or heart failure
- Less often: a urinary blockage or a sudden kidney injury
If your BUN is low
A low BUN is common and rarely a concern on its own. It often reflects a low-protein diet or drinking a lot of fluid.
Common reasons
- Eating little protein
- Drinking a lot of fluid
- Pregnancy
- Less often: severe liver disease or poor nutrition
What can throw it off
Not drinking enough and a high-protein diet in the days before can raise BUN.
Questions to take to your appointment
- 1Could low fluids or my diet explain this?
- 2Does my creatinine point the same way?
- 3Should we repeat it when I'm well hydrated?
Read together with
Doctors rarely read BUN alone. These usually sit next to it.
Quick answers
What is the BUN blood test?
BUN (Blood urea nitrogen): A waste product made when the body breaks down protein. Your liver turns leftover protein into urea, and your kidneys pass it out in urine. BUN measures the nitrogen part of that urea. It rises and falls with kidney function, but also with fluids and diet.
What is a normal BUN level?
For most adults, BUN is typically 6 to 21 mg/dL for women and 8 to 24 mg/dL for men. Some countries print it in mmol/L, so check the unit first. Labs differ a little, so the range printed next to your result is the one to go by.
What does a high BUN mean?
A mildly high BUN often comes from low fluids or a high-protein diet. Doctors read it with creatinine to see whether the kidneys are involved. Common reasons include not drinking enough, or losing fluid through sweat, vomiting or diarrhea; a high-protein diet or protein supplements; steroid medicines, or a recent illness, injury or surgery; and older age, as kidney filtering slowly falls. A doctor reads it together with your other results and how you feel.
What does a low BUN mean?
A low BUN is common and rarely a concern on its own. It often reflects a low-protein diet or drinking a lot of fluid. Common reasons include eating little protein; drinking a lot of fluid; pregnancy; and less often: severe liver disease or poor nutrition.
What can affect my BUN result?
Not drinking enough and a high-protein diet in the days before can raise BUN.
What should I ask my doctor about my BUN?
Questions worth taking to the appointment: Could low fluids or my diet explain this? Does my creatinine point the same way? Should we repeat it when I'm well hydrated?
What this page can’t do
It reads each number on its own.
Doctors read results together — ALT with AST, ferritin with hemoglobin, TSH with free T4. A pattern says more than any single flag.
It doesn't know you.
Your age, your medicines, how you feel and your last result all change what a number means.
It doesn't remember.
Close this page and your results are gone. That's on purpose: nothing was ever sent to us.
We also make Vita: Health Coach, an app for those parts. It reads your whole report with your medicines and history in mind, answers follow-up questions in plain words, and keeps your reports in one place — for you and for the people you look after.
Vita: Health Coach on the App StoreSources
- Mayo Clinic Laboratories — Blood urea nitrogen (BUN), serum
- MedlinePlus — BUN (blood urea nitrogen) test
- MedlinePlus — BUN blood test
Stuck on a word? See the medical words. How we choose our sources. More about Vita Health Coach.