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Causes of high and low ammonia in the blood
Medical expert of the article
Last reviewed: 06.07.2025
The determination of the concentration of ammonia in the blood in liver diseases is assigned the role of an indicator of liver shunting (i.e. a substance that normally enters from the intestines into the portal vein system and into the liver). Under pathological conditions, with the development of venous collaterals, ammonia enters the general blood flow system, bypassing the liver, and thus becomes an indicator of portal blood discharge.
In addition to shunt hyperammonemia, enzymatic hyperammonemia is also observed. The latter develops when the systems involved in the conversion of ammonia (enzymes of the urea cycle) malfunction. Such disorders are mainly recorded in children and adolescents and are observed much less frequently than shunt disorders. A distinction is made between congenital and acquired enzymopathies that lead to hyperammonemia. Congenital enzymopathies include hyperlysinemia (a defect in lysine dehydrogenase), propionic acidemia (a defect in propionic acid carboxylase), methylmalonium acidemia (a defect in methylmalonyl mutase), and ornithemia (a defect in ornithine ketoacid transaminase). Acquired enzymopathies include Reye's syndrome, which is characterized by particularly high hyperammonemia (3-5 times higher than normal).
Increased serum ammonia concentrations naturally occur in liver cirrhosis. In liver cirrhosis without encephalopathy, the ammonia concentration in the blood usually increases by no more than 25-50% compared to the upper limit of the norm, and in the development of encephalopathy - by 50-100%.
An increase in ammonia concentration is often observed in viral hepatitis. Severe hyperammonemia in such patients occurs with the development of acute liver failure, which is explained by the development of massive liver necrosis. Urea synthesis from ammonia is disrupted when more than 80% of the liver parenchyma is damaged. An increase in ammonia content in the blood is also observed in liver cancer, chronic active hepatitis, fatty degeneration, and the use of certain medications (barbiturates, narcotic analgesics, furosemide, etc.).