Urea

Some labs print a slightly higher upper limit for people over 65; the range is lower in pregnancy.

Urea is the waste product the liver makes when it breaks down protein from food and from the body's own tissues. It travels in the blood to the kidneys, which pass it into the urine. The test measures how much is in the blood at that moment.

It is part of the routine 'U&E' kidney test and is read alongside creatinine. It responds quickly to changes in hydration and protein intake, so it helps doctors tell a short-term change from a long-term one.

• Dehydration, which is the commonest reason for a mild rise in the general population
• Reduced kidney filtering
• A high-protein diet or protein supplements
• Bleeding into the gut, because the blood is digested as protein
• Steroid tablets and some water tablets
• Heart failure, where less blood reaches the kidneys

• A low-protein diet or poor appetite
• Pregnancy, because the blood volume expands and the kidneys filter more
• Liver conditions where less urea is made
• Drinking a lot of fluid before the test

• A dry day, a long fast, or a high-protein meal can move it outside the range with no change in the kidneys
• It rises a little with age in the general population
• A single value is far less telling than the trend

No fasting needed. Hydration on the day matters a great deal; a value taken when well hydrated is more representative.

Written by a UK consultant physician. Typical UK adult reference ranges; your laboratory's own printed range takes precedence.