Background/objective While ammonia plays a role in the complex pathophysiology of hepatic encephalopathy (HE), serum ammonia is unreliable for both diagnosis of, and correlation with, neurological symptoms in patients with cirrhosis. We aimed to quantify ordering, cost and appropriate use of serum ammonia in a major Midwestern healthcare system.

Design/method Serum ammonia ordering in adult patients presenting to a large Midwestern health system was evaluated from 1 January 2015 to 31 December 2019.

Results Serum ammonia ordering was prevalent, with 20 338 tests ordered over 5 years. There were no differences in the number of inappropriate serum ammonia tests per 100 000 admissions for chronic liver disease over time (Pearson’s correlation coefficient=−0.24, p=0.70). As a proportion of total ammonia tests ordered, inappropriate tests increased over time (Pearson’s correlation coefficient=0.91, p=0.03). Inappropriate ordering was more common at community hospitals compared with the academic medical centre (99.3% vs 87.6%, p<0.001).

Conclusion Despite evidence that serum ammonia levels are unreliable for the diagnosis of HE and are not associated with severity of HE in individuals with cirrhosis, ordering remains prevalent, contributing to waste and potential harm.