During the metabolism of protein in the body, the liver creates ammonia, which is broken down into a by-product called urea. Kidneys filter excess urea into the urine and in sweat, but some goes into the bloodstream as serum urea.
Serum urea concentration is important to determine if the kidneys are functioning correctly. A high level of serum urea means the kidneys are not filtering properly.
Low Serum Urea
If a patient presents a low serum urea level, it can indicate trouble with the liver. If the liver is not synthesizing protein, then urea will not be produced.
If a patient's serum urea level is higher than normal, it could mean the person is dehydrated. When the body is dehydrated, the kidneys will reabsorb more urea when ADH (antidiuretic hormone) is produced to reduce additional loss of fluids.
Diet can also affect serum urea levels. Depending whether a person has a high or low protein diet, it could alter the serum urea level, giving a false indication that there could be a kidney or liver problem.
Venous blood can be drawn and tested to determine serum urea levels. A normal serum urea level for adults is between 15 and 50 mg/dl.