Blood urea (azotemia): what it is, what it tells you and when it’s tested

Azotemia is the amount of urea in your blood. Urea is the waste your liver makes when your body uses protein. Your kidneys then clear it in your urine. So the value depends on what you eat, how much you drink and how well your kidneys work.

When it’s tested

In Italy, doctors often add it to routine blood tests, next to creatinine. They also order it with dehydration, vomiting or diarrhoea, before some medicines, or to follow kidney or liver disease.

On its own, though, it says little about your kidneys. It rises and falls with the protein you eat and the water you drink. To see how well the kidneys filter, guidelines use creatinine and the estimated filtration rate, eGFR.

That is why Rosa does not test blood urea. Instead it measures creatinine, eGFR, albumin in the urine and a urine test, which say more about your kidneys.

What it tells you, and what it does not

If it is high, your body is making a lot of urea or your kidneys are clearing too little. The most common causes are simple: you drank too little or ate a lot of protein.

On its own it does not say whether your kidneys are diseased. A high urea with a normal creatinine usually does not come from the kidneys. If both rise, your doctor looks more closely.

If it is low, it is almost never a problem.

That is why it is read together with other tests:

• Creatinine: It shows whether the kidneys are really involved
• eGFR: It estimates how well the kidneys filter
• Sodium: It helps show whether you are dehydrated
• Cystatin C: Another way to estimate filtration, if needed

Normal blood urea levels

The lab decides what is normal. For adults, a common reference gives 22 to 46 mg/dL. Many labs use wider limits, the upper one especially: the range on your own report is what counts.

Watch the unit. Some labs do not report urea but only the nitrogen it contains, called BUN or urea nitrogen. That number is about half: then the normal values are around 10.3 to 21.4 mg/dL. To go from BUN to urea, multiply by 2.14.

It rises a little with age and after meat-heavy meals. The blood test is done fasting from the evening before.

What your result means

Find the row for your result, in mg/dL of urea. If your report says BUN, multiply by 2.14 first. Which values need a doctor? Those above the limit on your report, especially if your creatinine is high too.

• Below 22: Low. Usually not a problem, and often still within your own lab’s range. It is common if you eat little protein or drink a lot. Less often, the liver is working less well. Usually nothing to do. If other liver tests are also out of range, talk to your doctor.
• 22 to 46: Normal. Your body makes and clears urea in balance. Nothing to do.
• Above 46: High. If it is only just above, check the limit on your report: many labs set it higher. Too little water or a lot of protein is often behind it, sometimes the kidneys or bleeding in the stomach. Talk to your doctor: they look at your creatinine and usually repeat the test. If it is far above the limit, see them soon.

If your blood urea is high or low

• High urea (azotemia): Too little water or a lot of protein is often behind it. Sometimes the kidneys. Creatinine tells them apart.
• Low urea: Usually not a problem. It is common with little protein or lots of water.

What can skew the result

A few things change it without the kidneys being involved. It helps to know them before your blood test.

• A protein-rich meal: Lots of meat, fish or protein supplements in the days before raise it. In the days before your test, eat as usual.
• Drinking too little: If you are dehydrated, from heat, sport or a fever, urea rises. It comes down once you drink again.
• Some medicines: Steroids and some diuretics can raise it. Do not stop them on your own: tell your doctor.
• Age: Urea rises a little over the years, even with healthy kidneys. The range on your report is what counts.

When to worry

Talk to your doctor if:

• Your urea is above the limit on your report and your creatinine is high too.
• It stays high when you repeat the test after drinking well.
• Your legs are swollen, you pass little urine or you feel very tired for no reason.
• You take blood pressure medicines, diuretics or anti-inflammatories every day.
• You vomit blood, have black stools, pass very little or no urine, or feel confused: call 112 or go to the emergency department.

Frequently asked questions

What are normal blood urea levels? For adults, a common reference gives 22 to 46 mg/dL, but many labs use wider limits. If your report measures BUN, the number is about half. The range on your own report is what counts.

Are azotemia and urea the same thing? In practice, yes. Azotemia is the Italian name of the test that measures urea in the blood. BUN measures only the nitrogen in urea, and is about half the number.

What is the difference between urea and creatinine? Both are waste products your kidneys clear. Urea changes a lot with diet and with how much you drink. Creatinine is steadier, so it shows better how well your kidneys filter.

Do I need to fast for a urea test? Yes. Usually you are asked to fast from the evening before. You can drink water.

Does Rosa test blood urea? No. Rosa measures creatinine, eGFR, albumin in the urine and a urine test, which say more about how your kidneys work. If your doctor wants blood urea, they order it separately.

Sources

• ISSalute, Italian National Institute of Health: Azotemia (blood urea test). ISSalute, Istituto Superiore di Sanità
• Hosten, BUN and creatinine. In: Clinical Methods: the history, physical, and laboratory examinations. Butterworths, 1990. PMID 21250147
• Simadibrata and colleagues, blood urea nitrogen-to-creatinine ratio to differentiate upper from lower gastrointestinal bleeding: a systematic review and meta-analysis. Journal of Gastroenterology and Hepatology, 2026. PMID 41555211
• KDIGO 2024 clinical practice guideline for the evaluation and management of chronic kidney disease. Kidney International, 2024. PMID 38490803