Initial Diagnostic Approach for Suspected Unknown Poisoning

Core Laboratory Assessment

Obtain serum electrolytes, bicarbonate, and calculate the anion gap, as an elevated anion gap can indicate toxic alcohol ingestion, salicylates, or other metabolic poisons, according to the American College of Critical Care Medicine 1
Perform arterial or venous blood gas analysis to assess pH, metabolic acidosis, and respiratory status, which helps identify toxidromes and guide management, as recommended by the American Thoracic Society 2, 1
An anion gap >27 mmol/L strongly suggests severe toxic alcohol poisoning requiring urgent intervention, based on evidence from the American College of Critical Care Medicine 1

Obtain carboxyhemoglobin level by co-oximetry on arterial or venous blood in patients with suspected carbon monoxide exposure, altered mental status, or exposure history, as recommended by the American Thoracic Society 2, 3, 4
Standard pulse oximetry is unreliable for detecting CO poisoning, as COHb reads similarly to oxyhemoglobin at 660 nm, often showing falsely normal oxygen saturation despite significant CO poisoning, according to the American Thoracic Society 2, 3
Noninvasive pulse CO-oximetry has poor sensitivity and should not be relied upon; laboratory-based spectrophotometry is required for diagnosis, based on evidence from the American College of Emergency Physicians 4, 5

Obtain a 12-lead ECG in all patients with suspected poisoning, particularly with chest pain, dysrhythmias, or ingestion of cardiotoxic agents, as recommended by the American Heart Association 6
ECG findings may reveal QRS widening, QT prolongation, or dysrhythmias that guide antidote therapy, according to the American Heart Association 6

If available, obtain serum glycolate concentration in suspected ethylene glycol poisoning, as levels >12 mmol/L indicate severe poisoning requiring extracorporeal treatment, based on evidence from the American College of Critical Care Medicine 1
Glycolate correlates with acute kidney injury and mortality better than ethylene glycol concentration itself, according to the American College of Critical Care Medicine 1
Be aware that elevated glycolate can falsely elevate lactate measurements on some analyzers due to cross-reactivity, potentially masking the true severity of toxic alcohol poisoning, as noted by the American College of Critical Care Medicine 1

Do not rely on pulse oximetry alone in suspected CO poisoning; it will appear falsely normal, as warned by the American Thoracic Society 2, 3
Do not delay treatment while awaiting laboratory confirmation if clinical suspicion is high; initiate supportive care and specific antidotes immediately, as recommended by the American Heart Association and the American Thoracic Society 2, 6