Serum Ammonia Cannot Grade Hepatic Encephalopathy: Use Clinical Scoring Systems
Serum ammonia levels alone do not add any diagnostic, staging, or prognostic value for grading hepatic encephalopathy in patients with chronic liver disease, and you should instead use the West Haven Criteria (WHC) or Glasgow Coma Scale (GCS) for clinical grading. 1
Why Ammonia Fails as a Grading Tool
The 2014 AASLD/EASL joint practice guidelines explicitly state that elevated blood ammonia does not correlate reliably with hepatic encephalopathy severity or grade. 1 While ammonia is mechanistically important in the pathophysiology of hepatic encephalopathy, the relationship between ammonia levels and clinical severity is non-linear and unpredictable. 2
Key limitations of ammonia for grading:
- Ammonia may remain elevated in cirrhotic patients without any encephalopathy symptoms 3
- Ammonia can stay elevated even after clinical resolution of hepatic encephalopathy 2
- Technical challenges with specimen handling frequently produce falsely elevated results 1
The Single Valid Use of Ammonia: Ruling Out Hepatic Encephalopathy
A normal ammonia level has high negative predictive value and should prompt immediate investigation for alternative causes of altered mental status. 2, 3 If you check an ammonia level in a patient with suspected overt hepatic encephalopathy and it returns normal, the diagnosis of hepatic encephalopathy is in question and you must search for other etiologies including:
- Intracranial hemorrhage (5-fold increased risk in cirrhosis) 1
- Septic encephalopathy 2
- Hyponatremia 2
- Wernicke's encephalopathy 2
- Medication effects 2, 3
- Alcohol withdrawal 3
Recommended Clinical Scoring Systems
Overt hepatic encephalopathy should be graded using the West Haven Criteria (WHC) or Glasgow Coma Scale (GCS), both validated clinical tools. 1
West Haven Criteria for Grading:
- Grade I: Trivial lack of awareness, shortened attention span, impaired addition/subtraction
- Grade II: Lethargy, disorientation to time, personality change, inappropriate behavior
- Grade III: Somnolence to semi-stupor, responsive to stimuli, confused, gross disorientation
- Grade IV: Coma, unresponsive to painful stimuli
These grades reflect the degree of self-sufficiency and need for care, which directly impacts patient morbidity and quality of life. 1
For Minimal/Covert Hepatic Encephalopathy:
Use validated psychometric and neurophysiological testing, not ammonia levels. 1 The guidelines recommend at least two validated testing strategies:
- Paper-pencil tests (PHES - Psychometric Hepatic Encephalopathy Score) 1
- Computerized tests (CRT, ICT, SCAN, or Stroop) 1
- Neurophysiological tests (Critical Flicker Frequency or EEG) 1
When Repeated Ammonia Measurements May Be Justified
Repeated ammonia measurements are only appropriate in research settings to assess the efficacy of ammonia-lowering drugs, not for routine clinical management. 2, 3 Serial ammonia values should not guide your therapeutic decisions or determine when to escalate or de-escalate treatment. 2
Critical Pitfall to Avoid
Do not delay empirical treatment while waiting for ammonia results. 2 Hepatic encephalopathy is a clinical diagnosis requiring immediate therapy with lactulose (titrated to 2-3 soft bowel movements daily), regardless of ammonia level. 2 The dose adjustment should be based on clinical response and stool frequency, not ammonia values. 2
Special Context: Acute Liver Failure
The one exception where ammonia has prognostic value is in acute liver failure (distinct from chronic liver disease), where arterial ammonia levels >200 µg/dL predict increased risk of cerebral edema and intracranial hypertension. 2, 4 This does not apply to the chronic liver disease population where ammonia monitoring has no clinical role. 2