Diagnostic Workup for Severe Acute Hyperammonemia of Uncertain Origin

Initial Assessment and Stabilization

The American College of Physicians recommends confirming hyperammonemia with accurate ammonia measurement from a free-flowing venous or arterial blood sample that must be properly collected and processed quickly to avoid false elevations 1
Secure airway, breathing, and circulation as hyperammonemia can progress to coma and respiratory failure, according to the American Heart Association 1
Assess neurological status using West Haven criteria or Glasgow Coma Scale to determine severity of encephalopathy, as suggested by the European Association for the Study of the Liver 2
Consider ICU admission for patients with moderate to severe encephalopathy (Grade 3 or 4 hepatic encephalopathy), as recommended by the European Association for the Study of the Liver 2

Obtain blood samples for complete metabolic panel including liver function tests to rule out liver disease, as recommended by the American Association for the Study of Liver Diseases 2
Plasma amino acid profile can identify patterns suggestive of urea cycle disorders, according to the National Institute of Diabetes and Digestive and Kidney Diseases 3, 1
Urine organic acids can identify organic acidemias, as suggested by the American College of Medical Genetics and Genomics 1
Plasma acylcarnitine profile can identify fatty acid oxidation disorders, according to the National Institute of Diabetes and Digestive and Kidney Diseases 1
Lactate and pyruvate levels can assess for mitochondrial disorders, as recommended by the Mitochondrial Medicine Society 3

Investigate common precipitants of hyperammonemia, such as infections, electrolyte disorders, acute kidney injury, alkalosis, dehydration, constipation, and medication review for potential triggers, as suggested by the European Association for the Study of the Liver 2

Stop protein intake temporarily to reduce nitrogen load, as recommended by the National Institute of Diabetes and Digestive and Kidney Diseases 4, 1
Administer intravenous glucose (8-10 mg/kg/min) to prevent catabolism, according to the American Diabetes Association 4, 1
Provide intravenous lipids (0.5 g/kg daily, up to 3 g/kg daily) for caloric support, as suggested by the American Society for Parenteral and Enteral Nutrition 4
Aim for caloric intake ≥100 kcal/kg daily to prevent protein breakdown, as recommended by the American Society for Parenteral and Enteral Nutrition 4

Consider hemodialysis if ammonia levels exceed 300-400 μmol/L despite medical therapy, as recommended by the American Society of Nephrology 1
Consider hemodialysis if neurological status rapidly deteriorates, according to the Neurocritical Care Society 1
Signs of moderate to severe encephalopathy can indicate the need for hemodialysis, as suggested by the European Association for the Study of the Liver 4

Genetic testing for urea cycle disorders and other inborn errors of metabolism can provide a definitive diagnosis, as recommended by the American College of Medical Genetics and Genomics 3
Enzyme activity assays in appropriate tissues (liver, red blood cells) can help diagnose urea cycle disorders, according to the National Institute of Diabetes and Digestive and Kidney Diseases 3
Brain imaging (MRI) can assess for cerebral edema if neurological symptoms are prominent, as suggested by the American Academy of Neurology 2, 1

Monitor ammonia levels every 2-4 hours initially until trending down, as recommended by the American Society of Nephrology 4
Assess neurological status continuously, according to the Neurocritical Care Society 2
Monitor electrolytes, especially sodium and potassium, as suggested by the American Heart Association 4
Monitor blood glucose to prevent hypoglycemia, as recommended by the American Diabetes Association 4
Monitor acid-base status, according to the American Society of Nephrology 4