serum ammonia

see also:

• hepatic encephalopathy

• ammonia is biosynthesised through normal amino acid metabolism and is important for normal animal acid/base balance but is toxic in high concentrations
• ammonia load is increased with high protein intake or GIT bleeding
• in fish and aquatic invertebrates, it is excreted directly into the water
• in mammals, sharks, and amphibians, the liver converts ammonia to less toxic urea via the urea cycle and then excreted in urine
  • liver failure may result in toxic levels of ammonia which contributes to the features of hepatic encephalopathy
• in birds, reptiles, and terrestrial snails, metabolic ammonium is converted into uric acid, which is solid, and can therefore be excreted with minimal water loss
• plants can use these excreted nitrogenous wastes to create new amino acids and proteins

• see hepatic encephalopathy
• toxic levels in mammals usually arise in those with liver impairment who then have:
  • an illness which exacerbates the liver impairment, and/or,
  • increased ammonia production load such as from high protein intake, GIT bleeding or a catabolic state causing protein breakdown such as hyperthermia, and sepsis / septicaemia
• in addition, some ammonia is excreted in faeces and urine
  • Thiazide diuretics impair ammonia excretion in urine
  • lactulose may increase fecal excretion of ammonia by increasing fecal acidity through increased fermentation of the lactulose