Carboxyhaemoglobin, blood gas

Diagnostic Use

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.

Department

Core Biochemistry

Delphic Registration Code

BGS or COHB

Synonyms

Carbon Monoxide, blood gas
COHb, blood gas
FCOHb, blood gas

Test Code

3068

Specimen Type

• Whole Blood

Specimen Requirements

Tube/Container Type:

Preferred

• Syringe

Acceptable

• Lithium Heparin - Non-gel (Green Cap)
• Lithium Heparin - Gel (Green Cap)

Preferred Sample Volume (ml)

5.0

Interferences

Administration of hydroxocobalamin has been shown to interfere with some carboxyhaemoglobin assays, leading to false negative results.

Additional Specimen Information

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.

Aliquot Instructions

Sample Type

• Whole Blood

Minimum Volume (ml)

0.2

Transport to Lab

Ambient (8 - 24 degrees Celsius)

Additional Referral/Aliquot Information

Aliquot Instructions: 200 uL in blood gas capillary. 5 mL heparinised blood - DO NOT OPEN.Fridge

Interpretation

Mild elevations in carboxyhaemoglobin are often seen in smokers.

The concentration of carboxyhaemoglobin correlates with the signs and symptoms of toxicity

Carboxyhaemoglobin	Severity	Clinical features
0.5-3%	Normal (non-smokers)
<9%	Normal (smokers)
10-20%	Mild	Dizziness, dyspnoea, headache
20-30%	Moderate	Vertigo, ataxia
>40%	Severe	Confusion, coma, seizures, death

Reference Intervals

Non smokers <1.5%

Smokers <9%

Test Method

Co-oximetry using dedicated blood gas analyser

Non-Funded Test Cost

$24.50 (Exclusive of GST)

Billing Code

3002

Contact Information

Enquiry Form