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Measuring blood levels of ammonia may predict hepatic encephalopathy

Researchers found that fasting levels of ammonia in the blood could predict the risk for experiencing an episode of hepatic encephalopathy or hepatic encephalopathy-related morbidity among patients with cirrhosis, according to published findings.

John M. Vierling, MD, FACP, professor of medicine and surgery, Baylor College of Medicine, Houston, Texas, and colleagues performed a retrospective analysis using data of 178 patients with cirrhosis randomly assigned Ravicti (glycerol phenylbutyrate, Horizon Pharma), an ammonia-lowering agent, or placebo for 16 weeks.

All patients had ammonia levels measured and blood samples extracted at baseline, as well as on days 7 and 14 of the study.

“There is controversy over the utility of measuring blood levels of ammonia in the management of patients with overt hepatic encephalopathy,” the researchers wrote.

Binary logistic regression analysis was used to predict probabilities of having a hepatic encephalopathy (HE) episode, based on ammonia values, and then a Cox proportional model was used to determine the risk for developing an HE episode in patients with baseline fasting ammonia levels less than 1.5-fold the upper limit of normal (ULN) compared with patients with fasting ammonia levels greater than 1.5-fold the ULN.

Overall, “the risk and frequency of HE episodes and HE-related hospitalizations were correlated with baseline (mean, 51 ± 6 μmol/L; ULN = 35 μmol/L)” values and with on-study fasting levels of ammonia, according to the research. These risks and frequencies increased at levels greater than 1.5-fold the ULN.

Further analysis showed that risk for experiencing an HE episode and ammonia exposure decreased in patients that received glycerol phenylbutyrate, despite the level at baseline.

The researchers concluded: “In analysis of data from a phase 2 study of the effects of glycerol phenylbutyrate in patients with cirrhosis, we found that fasting levels of [ammonia] in blood can identify patients at risk for HE-related morbidity. Patients with HE might benefit from [ammonia]-lowering therapy.”

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