Author information

1 Virginia Commonwealth University and McGuire VA Medical Center, Richmond, Virginia, USA.

2 Liver Center and GI Division, Massachusetts General Hospital, Boston, Massachusetts, USA.

3 Southern California Research Center, Coronado, California, USA.

4 Inland Empire Liver Foundation, Rialto, California, USA.

5 Medical University of South Carolina, Charleston, South Carolina, USA.

6 University of Texas Southwestern Medical Center, Dallas, Texas, USA.

7 Human Predictions LLC, Cambridge, Massachusetts, USA.

8 Synlogic Inc., Cambridge, Massachusetts, USA.

9 Texas Liver Institute, University of Texas Health San Antonio, San Antonio, Texas, USA.

Abstract

BACKGROUND: 

Ammonia levels are used to assess hepatic encephalopathy, but their levels are highly variable in clinical practice.

METHODS: 

We studied factors associated with variation in ammonia values in cirrhotic patients without previous hepatic encephalopathy and healthy volunteers (HVs).

RESULTS: 

Ammonia increased by 12% and 18% at 1 and 2 hour, respectively, after a protein meal in 64 cirrhotic patients (P < 0.001). In 237 HVs, ammonia levels varied significantly between sites (P < 0.0001). New site-specific ammonia upper limits based on HV levels using a strict analysis protocol differed from routinely used values. Correlation between paired fresh samples was high (r = 0.83) but modest between fresh and frozen samples (r = 0.62).

CONCLUSIONS: 

Sample handling, processing, and protein intake impact ammonia levels across sites.