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This test measures the portion of your hemoglobin that is bound to carbon monoxide, called carboxyhemoglobin. It is performed on a blood sample, often as part of co-oximetry, which can distinguish different forms of hemoglobin. Carboxyhemoglobin reflects recent exposure to carbon monoxide from sources such as smoke, engine exhaust, or poorly vented fuel-burning devices.
Both arterial and venous samples can be used, and the result helps your care team understand how much of your blood’s oxygen-carrying capacity is being blocked. The test is commonly paired with blood gas measurements to put the finding in clinical context.
Carbon monoxide binds to hemoglobin tightly, reducing the amount of oxygen delivered to your tissues and changing how readily oxygen is released. Measuring carboxyhemoglobin helps diagnose carbon monoxide exposure or poisoning, evaluate smoke inhalation, and monitor response to oxygen therapy. It can also document baseline levels in people who smoke or who have occupational exposures.
Identifying elevated carboxyhemoglobin promptly matters because symptoms can be nonspecific, ranging from headache and nausea to confusion or chest discomfort. Children, pregnant people, older adults, and those with heart or lung disease are more vulnerable to harm from exposure, so early recognition guides timely treatment and safety interventions.
Your result is interpreted alongside your symptoms, exposure history, physical exam, and other tests such as blood gases. Lower values are expected in people without recent exposure, while higher values suggest significant exposure or smoking. If your level is above what is expected for you, your clinician may recommend oxygen, observation, repeat testing, or consultation for specialized care depending on your condition and how quickly the value is changing.
Next steps often include removing or fixing the suspected source of carbon monoxide, reviewing workplace or home safety, and ensuring detectors are present and working. If you are pregnant or have heart or lung disease, your team may act more cautiously and monitor you more closely, even with modest symptoms, to protect you and, if applicable, your baby.
Reference intervals vary by laboratory, analyzer, methodology, population, and units. The ranges shown here are for education only. Always interpret your results against the reference interval printed on your own lab report.
Smoking cigarettes, cigars, cannabis, or using certain vaping devices exposes you to carbon monoxide and can raise results for several hours. Avoiding these before the test, when safe, makes the result easier to interpret.
Time spent near running engines, fuel‑burning heaters, fireplaces, or in smoke-filled spaces before the blood draw can increase levels. Breathing fresh air or receiving oxygen lowers levels over time, so timing relative to exposure matters.
Arterial and venous samples are both used, but clinical context differs. Delays to analysis, air contamination, or improper capping can affect co-oximetry. Prompt transport and analysis improve accuracy.
Exposure to methylene chloride solvents, certain dyes used in emergencies, severe jaundice, or marked lipemia can interfere with spectrophotometric readings. Rare hemoglobin variants or concurrent methemoglobinemia can complicate interpretation.
Anemia, heart or lung disease, and pregnancy change how your body tolerates carbon monoxide. Pregnant people and fetuses are particularly sensitive, so clinicians may use more cautious thresholds for action.
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