Related tests: Uric acid, Creatinine, Creatinine clearance, Albuminuria, urinalysis, eGFR
Clinical significance
Excess amino acids cannot be stored and are broken down, releasing ammonia; free ammonia is extremely toxic, especially to the brain, but the body efficiently converts it into a non-toxic molecule that is easily eliminated: urea.
Urea is formed in the liver and released into the circulation, and is then eliminated in the urine through glomerular filtration
An increase in serum urea is caused by reduced kidney function, which in turn may be due to reduced blood flow (congestive heart failure, severe dehydration), acute or chronic kidney disease, post-renal obstruction or a high-protein diet. Increased urinary urea excretion is associated with high-protein diets, hyperthyroidism and the post-operative period.
A decrease in serum and urine urea may be associated with low-protein, high-carbohydrate diets, severe liver failure and poisoning.
Clinical indications
Serum urea is indicated in the assessment of kidney function.
Sample type
The patient must have a blood sample taken.
Preparation
You must fast for at least 8 hours; a small amount of water is allowed. You must have been standing or sitting upright for at least 30 minutes.
Notes
A true increase in serum urea may be due, in vivo, to treatment with corticosteroids and nephrotoxic drugs; a true decrease in serum and urine may be caused by growth hormone administration.
Serum urea concentration increases with age and with the protein content of the diet.