Why and when to measure ammonemia in cirrhosis? - 20/03/18
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Highlights |
• | Measuring ammonemia is essential in the diagnostic work-up of hepatic encephalopathy and/or coma. |
• | Neurological symptoms with normal ammonemia should lead to reconsider the diagnosis of hepatic encephalopathy; differential diagnosis should be evoked and ruled out. |
• | Inborn error of metabolism, especially urea cycle disorders, should always be considered when ammonemia is highly elevated, even in the presence of liver disease (>100μmol/L). |
• | Elevated ammonemia in association with neurological symptoms should prompt to evaluate the possibility of liver disease or portosystemic shunt. |
• | Drug induced encephalopathy should always be considered, even in cirrhotic patients. |
Summary |
Hyperammonemia plays a key role in the pathophysiology of hepatic encephalopathy (HE) and most HE treatments are ammonia-lowering drugs. However, the usefulness of measuring ammonemia in routine practice remains controversial and not recommended systematically even when neurological symptoms are present. First, ammonemia measurement should be carefully performed in order to avoid a falsely elevated result. When performed, a normal ammonemia in a cirrhotic patient with neurological symptoms should lead to reconsider the diagnosis of HE. Indeed, literature data show that most cirrhotic patients with HE have an elevated ammonemia, which is however individually poorly correlated with the severity of symptoms. Nevertheless, elevated ammonemia seems to be a factor of bad prognosis in cirrhosis. A decrease in ammonemia after treatments is well proven but it is not determined whether it is associated with clinical efficacy. Repeated measurements could be useful in this context, especially in non-responders, to help differentiating other causes of encephalopathy, such as drug induced. In acute liver failure, the prognostic value of hyperammonemia is well described and could help an early recognition the most severe forms of this disease. We will also discuss how integrating ammonemia into the diagnostic work-up of liver failure and/or encephalopathy. Ammonemia is also essential to diagnose urea cycle disorders or drug toxicity that both need specific interventions.
Le texte complet de cet article est disponible en PDF.Keywords : Acute liver failure, Ammonemia, Cirrhosis, Hepatic encephalopathy, Urea cycle disorders
Abbreviations : Acute on chronic liver failure, Acute liver failure, Chronic liver failure, Electroencephalogram, Glutamine synthetase, L-ornithine L-acetate, Molecular adsorbant recirculating system, Model for end stage liver disease, Ornithine phenylacetate, Partial pressure of NH3, Proton pump inhibitors, Sensory evoked potentials, Urea cycle disorders
Plan
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