Urea

All parts of residual nitrogen represent final products of protein metabolism. Concurrently, the main final product of protein metabolism is a urea. Ammonia is the primary source of urea formation. Urea level shifts depend on the process of urea formation and its excretion. These processes are interconnected with metabolism of amino acids (arginine and glutamine). The level of blood urea is decreased in hepatocirrhoses, acute yellow atrophy, phosphorous, arsenical and other poisoning, affecting liver. In general, increase of the urea concentration is accompanied with increase of creatinine and filtration reduction.

Urea (also known as carbamide) is a waste product of many living organisms, and is the major organic component of human urine. This is because it is at the end of chain of reactions which break down the amino acids that make up proteins. These amino acids are metabolised and converted in the liver to ammonia, CO², water and energy. But the ammonia is toxic to cells, and so must be excreted from the body. So the liver converts the ammonia to a non-toxic compound, urea, which can then be safely transported in the blood to the kidneys, where it is eliminated in urine.

Urea and creatinine levels, together with electrolytes are used to evaluate kidney function and to monitor patients with various degrees of kidney failure or those receiving dialysis.

What does the result mean?

High urea levels suggest impaired kidney function. This may be due to acute or chronic kidney disease. However, there are many things besides kidney disease that can affect urea levels such as decreased blood flow to the kidneys as in congestive heart failure, shock, stress, recent heart attack or severe burns; bleeding from the gastrointestinal tract; conditions that cause obstruction of urine flow; or dehydration.

Low urea levels are not common although they can be seen in severe liver disease or malnutrition but other tests can be used to diagnose or monitor these conditions. Low urea is also seen in normal pregnancy.

Reference intervals

Female

< 4 years: 1.8 - 6.0 mmol/L

4 - 13 years: 2.5 - 6.0 mmol/L

14 - 19 years: 3.0 - 7.5 mmol/L

20 - 50 years: 2.5 - 6.7 mmol/L

> 50 years: 3.5 - 7.2 mmol/L

Male

< 4 years: 1.8 - 6.0 mmol/L

4 - 13 years: 2.5 - 6.0 mmol/L

14 - 19 years: 3.0 - 7.5 mmol/L

20 - 50 years: 3.2 - 7.4 mmol/L

> 50 years: 3.0 - 9.2 mmol/L

1.       https://pathologytestsexplained.org.au/ptests-pro.php?q=Urea

2.       https://www.ouh.nhs.uk/biochemistry/tests/tests-catalogue/urea.aspx

3.       https://www.vinmec.com/en/news/health-news/general-health-check/the-role-of-urea-determination-in-blood-and-urine/