Haemoglobin bound to carbon monoxide is known as carboxyhaemoglobin. Carbon monoxide has a higher affinity for haemoglobin than oxygen and thus high concentrations of carbon monoxide prevent O2 from binding to haemoglobin, reducing oxygen delivery to the tissues.
Carbon monoxide poisoning may be intentional or accidental (e.g. smoke inhalation from a house fire, exposure to vehicle exhaust fumes, household exposure from malfunctioning gas boiler etc.). Symptoms of carbon monoxide poisoning range from headache and fatigue in mild cases to hypoxia and decreased level of consciousness in severe cases.
Carboxyhaemoglobin can be measured by a co-oximetry module which is available on most blood gas analysers.
BGS or COHB
Carbon Monoxide, blood gas
COHb, blood gas
FCOHb, blood gas
Administration of hydroxocobalamin has been shown to interfere with some carboxyhaemoglobin assays, leading to false negative results.
It is best to collect a blood gas specimen, although testing can also be carried out on a lithium heparin tube (green top) which must be maximally filled. Tubes must not be uncapped before analysis.
Paediatric Specimen - 200 uL in a blood gas capillary is acceptable for testing.
Ambient (8 - 24 degrees Celsius)
Aliquot Instructions: 200 uL in blood gas capillary. 5 mL heparinised blood - DO NOT OPEN.Fridge
Mild elevations in carboxyhaemoglobin are often seen in smokers.
The concentration of carboxyhaemoglobin correlates with the signs and symptoms of toxicity
|10-20%||Mild||Dizziness, dyspnoea, headache|
|>40%||Severe||Confusion, coma, seizures, death|
Non smokers <1.5%
Co-oximetry using dedicated blood gas analyser
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