What is the test for cyanide poisoning?

From the Guidelines

Testing for cyanide poisoning should not be delayed, and treatment with hydroxocobalamin (preferred) or sodium nitrite plus sodium thiosulfate should be initiated immediately if poisoning is suspected, without waiting for confirmatory testing. This approach is based on the most recent guidelines from the American Heart Association, which emphasize the importance of prompt treatment in cases of suspected cyanide poisoning 1. The clinical presentation and history of exposure are crucial in making treatment decisions, as laboratory results may not be immediately available in emergency situations.

Key Diagnostic Considerations

• Blood tests to measure cyanide levels and lactate levels, which are often elevated in cyanide toxicity, can confirm exposure but may not be readily available.
• Arterial blood gas analysis showing metabolic acidosis with an elevated anion gap and venous oxygen saturation can provide supporting evidence.
• The presence of a bitter almond odor on the breath may be noted in some cases, though not everyone can detect this smell.
• Elevated lactate levels due to cellular hypoxia caused by cyanide's interference with oxygen utilization are a key laboratory finding.

Treatment Approach

• Hydroxocobalamin is the preferred antidote for cyanide poisoning, as it binds cyanide, converting it to less toxic compounds that can be excreted by the body 1.
• Sodium nitrite plus sodium thiosulfate is an alternative treatment option if hydroxocobalamin is not available.
• The decision to treat should be based on clinical judgment, considering the severity of symptoms and the likelihood of cyanide exposure, rather than waiting for laboratory confirmation.

Special Considerations

• Children are more vulnerable to cyanide poisoning due to their higher alveolar ventilation per minute and lower body mass index compared to adults 1.
• In cases of smoke inhalation, the measurement of plasma lactate concentration may guide the indications for hydroxocobalamin treatment, as plasma lactate concentration is correlated with plasma cyanide concentrations 1.

From the FDA Drug Label

There is no widely available, rapid, confirmatory cyanide blood test Treatment decisions must be made on the basis of clinical history and signs and symptoms of cyanide intoxication. The presence and extent of cyanide poisoning are often initially unknown.

Diagnosis of cyanide poisoning is based on clinical history and signs and symptoms of cyanide intoxication, as there is no widely available, rapid, confirmatory cyanide blood test. Key signs and symptoms include:

• Altered mental status (e.g., confusion, disorientation)
• Mydriasis
• Plasma Lactate Concentration ≥ 8 mmol/L
• Tachypnea/Hyperpnea (early) or Bradypnea/Apnea (late)
• Hypertension (early)/Hypotension (late) Treatment decisions should be made based on these clinical findings, and treatment should not be delayed to obtain a plasma lactate concentration if cyanide poisoning is suspected 2.

From the Research

Diagnosis of Cyanide Poisoning

• Cyanide poisoning can be diagnosed based on signs and symptoms such as headache, vertigo, agitation, confusion, coma, convulsions, and death 3
• Elevated plasma lactate, associated with cardiovascular collapse, should suggest cyanide intoxication 3
• Definitive laboratory confirmation is generally delayed, making rapid diagnosis and treatment crucial 3, 4

Treatment of Cyanide Poisoning

• Immediate treatment includes 100% oxygen, assisted ventilation, decontamination, correction of acidosis, and blood pressure support 3
• Antidotes for cyanide poisoning include oxygen, hydroxocobalamin, di-cobalt EDTA, and methaemoglobin-inducers 3
• Hydroxocobalamin is an attractive antidote due to its rapid cyanide binding and lack of serious side-effects, even in the absence of cyanide intoxication 3, 5, 6
• Sodium thiosulphate acts more slowly than other antidotes and is indicated in subacute cyanogen poisoning and as an adjunct to acute cyanide poisoning 3, 7

Antidote Efficacy

• The efficacy of hydroxocobalamin and sodium thiosulfate has been demonstrated in case reports, with combination therapy showing promise in reducing long-term neurological and visual sequelae 5, 6
• Hydroxocobalamin seems to be an appropriate antidote for empiric treatment of smoke inhalation and other suspected cyanide poisoning victims in the out-of-hospital setting 7
• The onset of antidotal action of sodium thiosulfate may be too slow for it to be the only cyanide antidote for emergency use 7