Urea - [also known as BUN]

Urea is a small molecule produced from protein and put out by the kidneys, so blood levels rise in kidney failure. It is not such an accurate test for kidney function as creatinine, but is a useful test when used together with creatinine, because it is affected by:

Normal = 3.6-5.0 mmol/l (20-30 mg/dl).

below 3.5
Low. Common explanations are low protein intake from diet, or liver disease. A low urea is normal in pregnancy.
High. Suggests kidney failure, dehydration, high protein intake, or bleeding. Levels over 8-10 are unlikely to be due to diet alone.
Very high - suggests serious illness or renal failure

Urea has given its name to 'uraemic', which means the symptoms and signs of kidney failure.

Urea on haemodialysis: dialysis treatments should cause a big drop in urea levels. This can be measured as the Urea Reduction Ratio (URR). The URR can be used to help to show whether enough treatment is being given.

More info about urea (BUN) from Lab Tests Online

This page created 6th December 2004, last modified July 9, 2015, on the PatientView website