- A nitrogen-containing compound that is normally cleared by the liver.
- Acute and chronic liver failure cause hyperammonaemia, and ammonia is one of the waste products present in hepatic encephalopathy. Serum ammonia may not necessarily be elevated in this condition, however, and the concentration has a poor correlation with severity of encephalopathy.
Causes of Hyperammonaemia
- Protein load - GI bleeding, TPN, multiple myeloma
- Protein catabolism - vigorous exercise, seizure, trauma, burns, starvation, corticosteroids
- Urease-producing bacteria - e.g. Escherichia, Proteus, Klebsiella
- Portosystemic shunt - liver failure, portal venous thrombosis, TIPS, congenital
- Drugs - valproate, carbamazepine, salicylates
- Inborn errors of metabolism - e.g. urea cycle disorders, organic acidurias, FAO defects
- Generally, protein loads and increased protein catabolism are insufficient to cause symptomatic hyperammonaemia unless they unmask an underlying urea cycle disorder.