Carbon monoxide (CO) is a colorless, odorless, and tasteless gas, making it virtually undetectable. Since symptoms of exposure often mimic those of the common flu, diagnosing carbon monoxide poisoning based on symptoms alone is unreliable. Specialized medical testing is the only way to confirm exposure to this toxic gas. This diagnostic approach is necessary for determining the proper course of treatment and assessing potential long-term health consequences.
How Carbon Monoxide Harms the Body
The danger of carbon monoxide lies in its immediate interference with the body’s oxygen transport system. When inhaled, CO bypasses the lungs and enters the bloodstream, where it targets the hemoglobin protein inside red blood cells. Hemoglobin’s job is to pick up oxygen from the lungs and carry it to tissues throughout the body.
Carbon monoxide binds to hemoglobin with an affinity approximately 200 to 250 times greater than oxygen. This strong bond creates a new compound called carboxyhemoglobin (COHb), which prevents hemoglobin from carrying oxygen. Even small concentrations of CO can rapidly convert a significant portion of the blood’s hemoglobin into COHb.
The formation of COHb leads to cellular hypoxia, or oxygen deprivation, throughout the body. Organs with the highest oxygen demands, such as the brain and the heart, are particularly vulnerable. CO also binds directly to other proteins, like myoglobin and mitochondrial enzymes, further impairing cellular energy production and function.
The Definitive Diagnostic Test
The definitive method for diagnosing carbon monoxide poisoning centers on measuring the concentration of carboxyhemoglobin (COHb) in the blood. This requires a blood sample, drawn from either a vein or an artery. The sample is analyzed using a co-oximeter, a specialized spectrophotometer that distinguishes between different forms of hemoglobin.
Standard pulse oximeters, which measure oxygen saturation, are unreliable in this scenario because they cannot differentiate between oxygen-carrying hemoglobin and COHb. This often results in a falsely normal reading. The co-oximeter precisely quantifies the percentage of total hemoglobin converted into carboxyhemoglobin. This blood analysis is the gold standard for diagnosis.
Non-invasive devices called pulse CO-oximeters can provide a rapid screening estimate using a finger sensor, but they are not precise enough for a definitive diagnosis. Treatment with supplemental oxygen, often started by emergency medical services before hospital arrival, can rapidly lower the COHb level. Consequently, a blood test performed hours after exposure or oxygen administration may show a deceptively low COHb percentage. Medical professionals must interpret the test result in the context of the patient’s symptoms and the time elapsed since exposure and the start of oxygen therapy.
Understanding Carboxyhemoglobin Levels
The percentage of carboxyhemoglobin in the blood helps medical teams understand the extent of the exposure, though it does not always correlate directly with the patient’s symptoms. For non-smokers in low-pollution areas, a normal COHb level is less than 3%. Cigarette smokers, due to chronic exposure, can have baseline levels ranging from 5% to 10%.
A COHb reading above 10% in a non-smoker generally confirms exposure, and levels are categorized to guide treatment decisions.
Levels of Poisoning
Mild poisoning is associated with levels between 10% and 20%, often presenting with headache and dizziness.
Moderate poisoning occurs between 20% and 40%, potentially causing severe symptoms like confusion, nausea, and impaired judgment.
Readings of 40% and above are considered severe, often leading to loss of consciousness, seizures, and cardiorespiratory compromise.
A patient’s COHb level can be significantly lower than expected if they received oxygen therapy before the blood draw. The COHb percentage serves as one piece of information, considered alongside the patient’s overall physical and neurological status.
Post-Diagnosis Care and Medical Intervention
Once carbon monoxide poisoning is diagnosed, treatment focuses on rapidly removing CO from the bloodstream to restore oxygen-carrying capacity. The standard treatment involves administering 100% oxygen, typically through a tight-fitting non-rebreather mask. This high concentration of oxygen speeds up the dissociation of CO from hemoglobin, shortening the half-life of COHb from several hours in room air to about 30 to 90 minutes.
For patients exhibiting severe symptoms, such as loss of consciousness, neurological impairment, or those who are pregnant, Hyperbaric Oxygen Therapy (HBOT) may be utilized. HBOT involves placing the patient in a specialized chamber where they breathe 100% oxygen at air pressures two to three times greater than normal atmospheric pressure. This process forces a large amount of oxygen directly into the blood plasma, independent of the compromised hemoglobin, to reach damaged tissues.
Beyond oxygen delivery, medical teams conduct additional tests to assess for organ damage caused by oxygen deprivation. An electrocardiogram (EKG) and cardiac biomarker tests, such as troponin levels, are performed to check for injury to the heart muscle. In cases of severe poisoning, neurological imaging like a CT or MRI scan may be required to look for evidence of swelling or damage in the brain. Follow-up care includes monitoring for delayed neurological symptoms, which can appear days or weeks after the initial exposure.