aka Metabolic Muddle 001
You’ve just been handed over a patient who has an altered mental status when the phone rings. It’s the lab – you’re told that your patient has a serum ammonia level of 250 umol/L (reference range, 11-35 umol/L).
Q. What are the possible causes of hyperammonaemia?
Except for obvious liver failure, hyperammonaemia is easily forgotten as a potential cause of metabolic encephalopathy. Ammonia is produced by the hepatic metabolism of amino acids and is primarily degraded via the urea cycle.
The causes of hyperammonemia include:
Overproduction of ammonia
Protein load
gastrointestinal hemorrhage
gastric bypass
multiple myelomaallogeneic stem cell transplantation
parenteral nutritionIncreased catabolism
starvation
seizures
vigorous exercise
burns
corticosteroidsUrinary
urease-producing infection (e.g. Proteus and Klebsiella spp.)
congenital ureteric obstruction associated with infection
Reduced eliminationLiver failure (acute or chronic)
Drugs and toxins
valproate
carbamazepine
salicylates
rifampicin
hepatotoxic drugs (e.g. paracetamol, halothane) and toxins (e.g. mushrooms)Metabolic errors
urea cycle disorders
organic acidemias
fatty acid oxidation disorders
In the absence of obvious liver dysfunction or a drug cause, metabolic errors should be considered. Some metabolic errors can go undiagnosed until adulthood.
Reference
- Crosbie DC, et al. Late-onset ornithine transcarbamylase deficiency: a potentially fatal yet treatable cause of coma. Crit Care Resusc 2009; 11:222-227
About Chris Nickson
