Measuring initial ammonia levels alone is not sufficient for accurately diagnosing hepatic encephalopathy (HE).
Serum ammonia levels
- The AASLD/EASL 2014 guidelines state that increased blood ammonia alone does not add any diagnostic, staging, or prognostic value for HE in patients with chronic liver disease
- However, the AISF 2019 guidelines recommend obtaining venous blood ammonia level measurement as part of the workup in all forms of new-onset unexplained delirium to aid in identifying unrecognized type B HE
- The EASL 2022 guidelines also recommend obtaining serum ammonia level measurement in patients with delirium or encephalopathy and liver disease, as a normal value brings the diagnosis of HE into question
Diagnosis of HE
- The AASLD/EASL 2014 guidelines recommend diagnosing overt HE based on clinical criteria
- They also recommend diagnosing HE by excluding other causes of brain dysfunction and obtaining a diagnostic workup considering other disorders able to alter brain function and mimic HE
- The AISF 2019 guidelines recommend excluding other causes of mental impairment through systematic and careful evaluation in order to diagnose type A HE
Neurophysiological and psychometric tests
- The AASLD/EASL 2014 guidelines suggest obtaining neurophysiological and psychometric tests by experienced examiners for the diagnosis and grading of minimal HE and covert HE
- They also suggest diagnosing and grading minimal HE and covert HE using several neurophysiological and psychometric tests, obtained by experienced examiners
Differential diagnosis
- The EASL 2022 guidelines recommend identifying alternative or additional causes of neuropsychiatric impairment in patients with suspected HE to improve prognostic accuracy and treatment results
- They also recommend recognizing that features of covert HE and mild cognitive impairment (MCI) of an etiology other than liver dysfunction show significant overlap
In conclusion, while serum ammonia levels can aid in the diagnosis of HE, they are not sufficient on their own. A comprehensive approach including clinical criteria, exclusion of other causes, and neurophysiological and psychometric tests is recommended for accurate diagnosis.