Ammonia Toxicity Workup

Updated: Dec 29, 2015
  • Author: Steven Issley, MD, FRCPC; Chief Editor: Asim Tarabar, MD  more...
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Approach Considerations

Serum ammonia levels are of little value in patients with ammonia toxicity because they do not correlate with clinical condition. However, patients with compromised hepatic function may show increased serum ammonia levels because of less efficient metabolism.

Laboratory studies in patients with ammonia exposure include the following:

  • Serum acetaminophen level in intentional exposures
  • Complete blood count (CBC)
  • Electrolytes, blood urea nitrogen (BUN), and creatinine
  • Serum lactic acid
  • Serial arterial blood gases (ABGs) in cases of significant respiratory distress - Metabolic acidosis, respiratory alkalosis, increased alveolar-arterial gradient

Patients with eye injury should have a slit-lamp examination with fluorescein staining. Perform tonometry to determine if intraocular pressure is elevated. Measure conjunctival pH.

Depending on the clinical presentation, other tests and procedures may include the following:

  • Chest radiography
  • Abdominal series – To rule out perforation following ingestion
  • Cardiac monitoring
  • Pulse oximetry
  • Pulmonary capillary wedge pressure (PCWP) monitoring – In cases of severe acute lung injury (ALI) or acute respiratory distress syndrome (ARDS)
  • Pulmonary function tests (PFTs)
  • Ventilation/perfusion (V/Q) scan
  • Bronchoscopy – In severe acute inhalation injury
  • Endoscopy – In significant ingestion exposures

Pulmonary Testing

Once the acute emergency is controlled, PFTs are useful to gauge the severity of injury and to monitor progress and recovery. PFTs may show obstructive lung disease (in both acute and chronic cases) or restrictive lung disease (in chronic cases).

A V/Q scan may be useful to gauge the severity or progression of disease, but the results are unlikely to change acute management. Ventilation deficits generally are more pronounced in the larger airways. The ventilation scan also may show abnormal air trapping in the setting of lower airway obstruction.



Perform bronchoscopy to assess respiratory tract damage following acute inhalation injury (in severe cases). Bronchoscopic findings may include the following:

  • Airway edema, obstruction, and necrosis
  • Epithelial sloughing
  • Laryngitis and tracheitis
  • Diffuse alveolar damage


Consider endoscopy for significant ingestion exposures (large volume and/or industrial concentrations). Indications are somewhat controversial; obtain a GI consultation if needed. Perform endoscopy on symptomatic patients and patients with intentional exposure within 48 hours following ingestion. The risk of perforation increases if endoscopy is performed more than 72 hours post ingestion.

Findings on endoscopy may include the following:

  • Laryngeal and epiglottic edema
  • Friable erythematous esophagus
  • Corrosive injury