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serum ammonia


  • 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


  • 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
ammonia.txt · Last modified: 2019/06/27 17:09 (external edit)