Platform
Company
Blood Gases
Review status
Currently under review
Pending specialist review and validation.
This test measures the fraction of your hemoglobin that is bound to carbon monoxide, called carboxyhemoglobin (COHb). Hemoglobin normally carries oxygen; when carbon monoxide is present, it competes with oxygen and forms COHb, which cannot deliver oxygen to tissues.
In a mixed venous sample, blood is taken from a catheter that collects blood returning from the body to the lungs. This provides an overall picture of how much carbon monoxide is bound across the body rather than at a single site. The measurement is performed by co-oximetry as part of blood gas analysis in critical care or during evaluation for possible carbon monoxide exposure.
Carbon monoxide exposure can occur from smoke inhalation, faulty heaters, vehicle exhaust, or other combustion sources. Elevated COHb reduces the blood’s ability to carry oxygen and can cause headache, dizziness, chest pain, confusion, or more severe symptoms. Measuring COHb helps confirm exposure, assess severity, and guide treatment such as high-flow oxygen or hyperbaric oxygen therapy.
Clinicians may order the mixed venous COHb test in intensive care settings when a catheter is already in place, after suspected exposure, during fire or smoke incidents, or to monitor response to therapy. People who smoke often have higher baseline COHb, so your clinical context and exposure history are essential for interpretation.
Your result is interpreted alongside your symptoms, exposure history, and other blood gas measurements. Lower values are expected in people without recent exposure, while higher values suggest exposure or increased production. If you receive oxygen therapy before the test, the value may decrease as carbon monoxide is cleared from the blood.
If your result is higher than expected, your care team will focus on removing you from any potential source, providing oxygen, and monitoring you for any symptoms. Repeat measurements can help confirm that levels are trending down with treatment. If the result does not match your history or symptoms, your clinician may review the sample type, timing, and any factors that could affect accuracy, and consider follow-up testing.
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.
Cigarettes, cigars, hookah, or wildfire and structure fire smoke can raise COHb and influence interpretation, even without obvious symptoms.
Breathing supplemental oxygen speeds clearance of carbon monoxide from hemoglobin, so levels can fall quickly and appear lower than at the time of exposure.
This test uses mixed venous blood; results can differ from arterial or peripheral venous samples. Mislabeling or using a different sample type can affect interpretation.
COHb declines over time, especially with oxygen. A delay between exposure and blood draw may reduce the measured level compared with the peak.
Dyes such as methylene blue, severe lipemia, or high bilirubin can affect some co-oximeters. Concurrent dyshemoglobinemias may also complicate interpretation.
Pregnancy and newborn physiology can alter risks from carbon monoxide. Clinicians may act with more caution even at modest elevations in these groups.
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