Ammonia, Blood

Ammonia is a waste product that forms as a result of nitrogen breakdown during intestinal protein metabolism and from digestion of blood which may be in the gastrointestinal tract (such as from esophageal varices). Another major source of ammonia is from the synthesis and conversion of glutamine by the renal tubules. In the kidneys, ammonia serves as an important renal buffer.
Normally, ammonia is converted into urea by the liver and then excreted by the kidneys. If a physical disorder prevents this conversion from occurring, the ammonia accumulates in the bloodstream. Toxic levels of ammonia in the blood lead to a problem known as hepatic encephalopathy, in which brain function is affected by the high ammonia levels. Correlation between plasma ammonia and the degree of encephalopathy can be erratic. For example, an individual with very high blood ammonia may show minimal or no effect while another may be greatly affected. The test can be used to determine whether liver dysfunction is the cause of such symptoms as confusion, excessive sleepiness, coma, or hand tremor. It can also be used to monitor the effectiveness of treatment for liver disease, such as cirrhosis.