Overview
A nitrogen-containing compound that is normally cleared by the liver.
Hyperammonaemia
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
Increased Production
- Protein load - GI bleeding, TPN, multiple myeloma
- Protein catabolism - vigorous exercise, seizure, trauma, burns, starvation, corticosteroids
- Urease-producing bacteria - e.g. Escherichia, Proteus, Klebsiella
- Sepsis
Reduced Elimination
- 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.
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