Urea

Urea is a waste product of protein breakdown produced in the liver and excreted by the kidneys. The test measures blood urea and is most often performed alongside creatinine to assess kidney function and the body’s fluid status.

Who the test is for

• people having general or preventive check-ups, alongside creatinine;
• people with chronic kidney disease, diabetes, high blood pressure or heart disease, for monitoring;
• people with vomiting or diarrhoea and suspected dehydration;
• people taking medicines that may affect kidney function;
• people before contrast-enhanced imaging and certain procedures when the facility requests urea and creatinine results.

What urea indicates

When the body breaks down proteins from food and its own tissues, ammonia is produced and converted to urea by the liver. Urea travels through blood to the kidneys and is excreted in urine. Its blood level therefore depends on three things: how much protein the body breaks down, liver function and how well the kidneys excrete urea.

Urea is therefore not a good standalone kidney test. It changes with diet, fluid intake and many conditions outside the kidneys, and is often still normal in early kidney damage. A more reliable indicator is creatinine and the estimated glomerular filtration rate (eGFR) calculated from it, printed alongside creatinine on the report. Urea adds information, for example about dehydration.

Panels including this test

Test Urea is also included in these panels.

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All panels including Urea (16) ›

Preparation and sample

Urea is measured in venous blood. Fasting is not required, but if glucose, lipids or PT are also measured that day, come in the morning after fasting. Drink water as usual because dehydration temporarily raises urea.

Because urea is almost always tested alongside creatinine, avoiding meat for 12 hours beforehand is helpful: British NICE guidelines recommend this before creatinine measurement because cooked meat temporarily raises it. A very large protein-rich meal can also slightly raise urea.

How results are interpreted

Urea is expressed in mmol/L. The reference interval depends on age and method and is printed on your report. Values are somewhat higher in older people and lower in children and pregnancy. A doctor interprets urea alongside creatinine and eGFR, not alone.

High urea

• Dehydration: after vomiting, diarrhoea, heat or insufficient fluid intake. Urea then often rises more than creatinine.
• Reduced kidney function, acute or chronic. Both urea and creatinine are usually high and eGFR low.
• Reduced blood flow through the kidneys, for example in heart failure.
• Obstructed urine flow, for example due to an enlarged prostate or stone.
• Upper digestive tract bleeding: blood is broken down in the intestines like other proteins, raising urea. Black, tarry stool or vomiting blood requires urgent assessment.
• Increased protein breakdown: a very high-protein diet, high fever, burns, serious illness or corticosteroid treatment.

Low urea

Low urea is rarely a cause for concern. It is common with low-protein diets, pregnancy, in children and with higher fluid intake. Less often it results from severe liver disease or malnutrition, when other results such as albumin and liver tests are also abnormal.

Urea and creatinine before CT or MRI

Intravenous contrast agents used in CT and MRI are excreted through the kidneys. The imaging facility therefore often requests creatinine results, usually tested alongside urea. Creatinine and eGFR are key to assessing contrast safety. Check with your imaging facility how recent results must be.

How to arrange testing

You can have blood taken without an appointment or referral at one of our branches across Croatia (listed on the Contact page). Prices for all tests and panels are available in the service price list. Urea and creatinine are best measured from the same blood sample.

Frequently asked questions

What does high urea with normal creatinine mean?

Most often dehydration or higher protein intake, and less often digestive tract bleeding or increased protein breakdown due to illness. Normal creatinine and eGFR suggest kidney filtration is probably preserved. A doctor assesses whether testing should be repeated after fluid replacement.

Are urea and ureja the same?

Yes. They are the same substance, and both names appear on reports. In some countries, such as the USA, blood urea nitrogen (BUN) is reported instead, usually in mg/dL, so these numbers cannot be directly compared with urea expressed in mmol/L.

Is urea enough to assess kidney function?

No. Creatinine and eGFR are the basic tests for kidney function, alongside urinalysis and, in diabetes and high blood pressure, urine microalbumin. When eGFR is unreliable, a doctor may request creatinine clearance.