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Blood urea nitrogen; BUN
To evaluate kidney function and monitor the effectiveness of dialysis
Test is performed frequently as part of a panel to check kidney function and may be requested as part of a general check up (U&E)
A blood sample drawn from a vein in the arm
As protein is broken down by the body it forms toxic products, which need to be eliminated form the body. The liver converts these products to non-toxic urea. Urea is then circulated in the blood to the kidneys where it is eliminated from the body.
Healthy kidneys eliminate more than 90 per cent of the urea the body produces, so blood levels may indicate how well your kidneys are working.
A blood sample is drawn from a vein in the arm.
No test preparation is needed.
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.
Patients of any age may undergo this test indicating the importance of the urea level as a part of the detoxification processes of the liver and excretory function of the kidneys.
Urea may be used in a panel of tests:
Urea is often ordered with creatinine:
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.
Urea levels may increase with age and also with the amount of protein in your diet. High-protein diets may cause abnormally high urea levels. Very low-protein diets can cause abnormally low urea. Lower urea levels are also seen in infants and small children.
Drugs that impair kidney function may increase urea levels and monitoring of this test may be performed.
Urea and creatinine are often the first tests that are used to check how well the kidneys are able to filter waste products from your blood.
A full U&E profile including electrolytes may allow further investigation of kidney function.
Tests: Creatinine, electrolytes, eGFR
Conditions: Kidney disease
RCPA Manual: urea
Kidney Health Australia
Last Review Date: January 13, 2020