• hepatic encephalopathy

Ammonia is key in the development of hepatic encephalopathy. A clear relationship between the degree of hyperammonemia and worsening encephalopathy is well-established in acute liver failure. The utility of ammonia testing in the diagnosis of overt hepatic encephalopathy (OHE), however, has been repeatedly questioned. First, the route (venous or arterial), laboratory and prandial state all contribute to wide variations in ammonia levels.1 Second, the correlation between ammonia levels and stage of OHE is only modest with many patients with ‘normal’ levels presenting with clinically high-grade encephalopathy.2 Lastly, hepatic encephalopathy is a clinical diagnosis dependent on a history and physical examination; as such, ammonia is notably absent from diagnostic and grading algorithms. Therefore, since ammonia levels are often not clinically relevant, its frequent misuse can result in excess healthcare costs. To answer the question of the impact of excessive ammonia ordering, Aby et al explore the prevalence and resulting financial consequences of inappropriate ammonia testing.3