text: reason for high ammonia levels in humans? i have a friend who was treated in a hospital because of high ammonia blood and ? urine ammonia levels. in humans and most other mammals, ammonia is produced in the bloodstream when mitochondria (the power plants of cells) break down amino acids for energy. the left over chemicals combine to form ammonia. ammonia is normally converted to a chemical compound called urea by the liver. if the liver is not functioning in this regard, or if liver failure occurs, a high ammonia level can result. other symptoms of liver failure include jaundice (a yellowing of the skin and the whites of the eyes).