Kidneys, electrolytes and minerals
Urea blood test: what a high or low result means
What a urea (or BUN) blood test measures, what high or low urea can mean, and what to ask your doctor.
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Explain my results → Available on web, iOS & Android.What is urea?
Urea is a waste product made in your liver when your body breaks down protein. Your kidneys remove it from the blood into your urine. Urea is part of the U&E (urea and electrolytes) blood test in the UK. In the US, a related test called BUN (blood urea nitrogen) is used, which measures the nitrogen in urea and is reported in different units.
Why is this test done?
- To check kidney function
- To check whether someone is dehydrated
- When someone is unwell, for example with vomiting or bleeding
- To monitor long-term conditions and medicines
What does a high urea mean?
A high urea can mean your kidneys are filtering less well, or that something else is raising it, such as dehydration.
Possible reasons include:
- Dehydration
- Kidney disease
- A high-protein diet
- Bleeding in the upper gut, such as from a stomach ulcer
- Some medicines, such as steroids
- Heart failure
What does a low urea mean?
A low urea is uncommon and is usually not a concern.
Possible reasons include:
- A low-protein diet or malnutrition
- Pregnancy
- Drinking a lot of fluid
- Severe liver disease, which reduces urea production
Why we don't list a "normal range". Reference ranges differ between laboratories and can depend on your age, sex and whether you are pregnant. The range printed next to your result on your own report is the one that applies to you, so use that, and talk to your doctor about what your result means for you.
What can affect your urea result?
- How much fluid you have been drinking
- How much protein you eat
- Recent bleeding in the gut
- Steroid medicines
Make sense of the whole report, not just one line
Results are easier to understand together. Patiently AI explains your report as a whole and writes personalised questions for your next appointment.
Try it with your own results → Paste, upload or photograph your results.Questions to ask your doctor
- Could dehydration explain my urea result?
- What do my creatinine and eGFR show about my kidneys?
- Do I need a repeat test?
- Should I change how much I drink or my diet?
Frequently asked questions
What is the difference between urea and BUN?
They measure the same waste product in different ways. The UK reports urea, while the US reports blood urea nitrogen (BUN), which counts only the nitrogen in urea. The numbers and units are different, so they cannot be compared directly.
Is urea a good test of kidney function on its own?
Not really, because diet, hydration and bleeding all affect it. Doctors look at urea alongside creatinine and eGFR.
Does high urea always mean kidney problems?
No. Dehydration is a very common cause, and a high-protein diet or steroids can raise it too.
Can Patiently AI explain my urea result?
Yes. Paste your results, or upload a photo, PDF or Word file, and Patiently AI explains them in plain English, sticking to the numbers and ranges on your own report rather than adding its own, and suggests questions to ask your doctor. It is free, needs no account, and removes identifying details on your device first.