aka Metabolic Muddle 010
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).
Q1. What are the possible causes of hyperammonaemia?
Answer and interpretation
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 myeloma
- allogeneic stem cell transplantation
- parenteral nutrition
- Increased catabolism
- vigorous exercise
- urease-producing infection (e.g. Proteus and Klebsiella spp.)
- congenital ureteric obstruction associated with infection
- Liver failure (acute or chronic)
- Drugs and toxins
- hepatotoxic drugs (e.g. paracetamol, halothane) and toxins (e.g. mushrooms)
- Metabolic errors
- urea cycle disorders
- organic acidaemias
- 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.
- Crosbie DC et al. Late-onset ornithine transcarbamylase deficiency: a potentially fatal yet treatable cause of coma. Crit Care Resusc. 2009 Sep;11(3):222-7. [PMID 19737127]