Clinical Significance

The major source of circulating ammonia is the gastrointestinal (GI) tract. Under normal conditions, ammonia is metabolized to urea by liver enzymes. Several diseases, both inherited and acquired, cause elevated ammonia (hyperammoneamia). The inherited deficiencies of urea cycle enzymes are the major cause of hyperammonemia in infants. Acquired hyperammonemia most often results from liver disease, renal failure and Reye’s syndrome. Elevated ammonia is toxic to the central nervous system. Plasma ammonia is measured by either chemical or enzymatic methods. The enzymatic method, which is simple and specific, is the most frequently used.