Tests
1st tests to order
carboxyhemoglobin level
Test
Patients with suspected exposure to CO should have their CO-Hb level measured by laboratory blood gas CO-oximetry (drawn from venous or arterial blood). The result is generally reported as a CO-Hb level. It is important to note how much time has elapsed since the patient has left the site of CO exposure, as CO-Hb levels may decrease with time and treatment, and may not reflect the true severity of the exposure.[27] However, CO-Hb is extremely stable so if CO-oximetry cannot be immediately obtained, anticoagulated blood samples obtained at the time of presentation can be analyzed later if necessary. Recommendations from national poison centers or local government agencies should be followed regarding CO-Hb levels. In the US, the Centers for Disease Control and Prevention (CDC) suggests that an elevated CO-Hb level of 2% in people who don’t smoke, and >9% for those who smoke, strongly supports a diagnosis of CO poisoning.[27] The CDC further states that CO-Hb levels do not correlate well with severity of illness, outcomes or response to therapy; therefore, to determine type and intensity of treatment, clinical symptoms should always be carefully assessed and a detailed history of exposure taken.[27] Although pulse CO-oximetry provides rapid bedside estimation of CO-Hb, it may be associated with significant error.[32][43][44] Therefore, some professional organizations do not recommend pulse CO-oximetry for the diagnosis of CO poisoning in patients with suspected CO toxicity.[30] However, the pulse CO-oximeter can serve as a helpful early screening tool until definitive measurement of a blood sample is available.
Arterial sampling is not necessary as there is a high correlation between venous and arterial samples.[28]
CO-Hb levels may decrease with time and treatment and may not reflect the true severity of the exposure.[16][17] However, CO-Hb is extremely stable, thus if CO-oximetry cannot be immediately obtained, anticoagulated blood samples obtained at the time of presentation can be analyzed later where there is an available machine.
Result
elevated level of 2% for people who do not smoke; >9% for those who smoke
ECG
cardiac monitoring
blood glucose
Test
Neurologic outcomes following CO poisoning are worse in patients with hyperglycemia.[33]
Result
may be elevated
complete blood count
Test
Request a complete blood count; check WBC count.
Result
may show leukocytosis
urea and electrolytes
Test
Take blood for urea and electrolytes.
Result
may be deranged
creatinine
Test
Acute kidney injury is a feature of carbon monoxide poisoning. See Acute kidney injury.
Result
may be elevated
lactate
Test
Severe exposures are associated with higher lactate levels. High lactate levels should raise suspicion for concomitant cyanide poisoning. This is especially the case if CO exposure is from a house fire, as cyanide may be produced from burning synthetic plastics.[47]
Result
may be elevated in severe poisoning; associated with low oxygen delivery or systemic hypoperfusion
pH level
Test
Severe exposures are associated with low pH levels (metabolic acidosis). Blood gases may be measured from arterial or venous blood.
Result
may be low in severe poisoning
cardiac biomarkers
creatine kinase
Test
Provides evidence of skeletal muscle damage. Creatine kinase level greater than five times the normal level, or more than 1000 IU/L indicates rhabdomyolysis. See Rhabdomyolysis.
Result
may be elevated
Tests to consider
chest x-ray
Test
Cardiomegaly, increased pulmonary vasculature, and increased alveolar markings.
Result
signs of noncardiogenic pulmonary edema
Mini Mental State Examination
Test
This is for assessment of cognitive function during the episode and at follow-up.[27]
Result
may be abnormal
CT head
Test
CT scan may be necessary, as determined by the treating physician, when patients present with acute neurologic symptoms such as confusion, headache, blurred vision, seizure, and/or coma.
Result
may see focal lesions and/or cerebral edema
magnetic resonance imaging and spectroscopy
Test
Magnetic resonance spectroscopy, may indicate sequelae from CO poisoning and can be considered.[36][37] On diffusion weighted imaging and fluid attenuated inversion recovery (FLAIR), the most commonly involved areas are the globus pallidus, caudate nuclei and periventricular white matter. The hippocampi can also be involved.[50]
Result
may be abnormal
liver function tests
Test
Should be considered in patients with severe poisoning. Derangement may indicate liver ischemia.
Result
may be deranged
pregnancy test
Test
Should be ordered in all women of childbearing age with suspected CO poisoning.[27] This is particularly important for moderate or severe poisoning. Exposure to CO during pregnancy can cause harm to the fetus.
Result
positive in pregnancy
Use of this content is subject to our disclaimer