BUN test: blood urea nitrogen, normal range and what it means

A BUN test measures blood urea nitrogen: the nitrogen carried in urea, a waste product made when the body breaks down protein. The kidneys clear urea from the blood, so the level gives a rough read on kidney function, but it also moves with hydration, diet and the liver. That is why BUN is usually read next to creatinine rather than on its own.

What it measures

When the body uses protein, nitrogen is left over. Liver cells turn that nitrogen into urea through a sequence of reactions called the urea cycle, and the kidneys pass the urea out in the urine. If the kidneys filter less, urea builds up in the blood. If the liver makes less, or there is less protein to process, the level falls.

A "urea test" and a "BUN test" describe the same substance reported two ways. Some laboratories report urea itself in millimoles per litre (mmol/L); others report BUN, the nitrogen part of it, in milligrams per decilitre (mg/dL). To turn BUN in mg/dL into urea in mmol/L, multiply by 0.357. A result printed as urea in mg/dL is a third version: for the same blood it reads a little over twice the BUN figure, so check which one your report uses before comparing it with a range.

Normal range

A commonly quoted adult range for BUN is 6 to 20 mg/dL, which works out to roughly 2.1 to 7.1 mmol/L of urea. BUN differs between men and women and usually rises with age. Ranges vary by laboratory, so read your result against the range printed on your own report.

What a high result usually points to

A high BUN usually points to one of three things: the kidneys clearing less, the body having less water, or more protein than usual reaching the blood to be processed.

• Kidneys clearing less: kidney disease, reduced blood flow to the kidneys, or a blockage in the urinary tract.
• Less water: dehydration raises urea in the blood.
• More protein to process: a high-protein diet, or bleeding in the stomach or intestines.
• The heart and circulation: heart failure, a recent heart attack, or shock.
• Other causes: burns and certain medicines.

An abnormal BUN does not always mean a condition that needs treatment. A doctor typically reads it against creatinine and eGFR, because comparing BUN with creatinine from the same sample helps find the cause: when both are up, the question is about kidney filtering, and when urea has risen on its own, fluids, protein intake, bleeding and medicines come into the picture. Talk to a doctor about a high result, with the result in front of you.

What a low result usually points to

A low BUN usually reflects little protein in the diet, poor nutrition, liver disease, or a lot of fluid. Because the liver makes urea, people with liver disease can have a low BUN even when their kidneys work normally, so a doctor reads a low result next to the liver tests and what you eat.

What moves it

• Protein intake. A high-protein diet raises it and a low-protein diet lowers it.
• Fluids. Dehydration raises it, and over-hydration lowers it.
• Age and sex. BUN differs by sex and usually rises with age.
• Medicines. Many medicines can interfere with the result. Mention them, and keep taking prescribed medicines unless your doctor has told you otherwise.
• Illness and injury. Burns, bleeding in the gut and heart failure all raise it.
• Units. A urea result in mmol/L, a urea result in mg/dL and a BUN result in mg/dL are three different numbers for the same blood. Comparing results from two laboratories means putting them in the same units.

Preparing for the test

A BUN test usually needs no special preparation. It is often drawn with tests that need fasting, so follow the instructions for the whole panel. Drink water as you normally would, and tell the person taking the sample about any medicines and protein supplements.

How Clare's panel handles it

In Clare's panel, urea (listed as Urea / Blood Urea Nitrogen) is measured by the lab. Clare uses it with creatinine to calculate the BUN/creatinine ratio, converting both to mg/dL before dividing BUN by creatinine. When Clare opens, members will see urea, creatinine and eGFR side by side, with their past results.

Price

BUN is usually sold within a kidney function test rather than on its own. When we read public prices on 11 October 2026, a kidney function test cost from 89 to 900 at six UAE providers. Five of the six were 250 or less, and the top of the range was a specialised package. VAT was rarely stated, some figures were offer or "from" prices, and home collection can add a fee.

Related tests

BUN is read with creatinine, which the kidneys clear in the same way but which comes from muscle rather than from protein in the diet; with eGFR, the estimate of filtering calculated from creatinine; and with the BUN/creatinine ratio, which sets the two against each other. Albumin, made by the liver like urea, helps when BUN is low. For preparing for a full panel, see Comprehensive blood test in Dubai: what to expect.

Why the number means more over time

Because urea moves with what you ate and drank, one result is partly a snapshot of that day. Results drawn under similar conditions, with the same fasting and ordinary fluids, are the ones that show a trend, and a rise in BUN that travels with a rise in creatinine means more than either alone. KDIGO advises checking for a recent meat meal, a change in muscle mass or extreme activity before reading a change in eGFR as a change in the kidneys; for urea, protein intake and fluids are the equivalent things to check. For people with chronic kidney disease, KDIGO recommends checking kidney function at least once a year.

Clare is opening with a waitlist at clare.health.