CO-Oximetry, haemoglobin and dyshaemoglobin analysis
POCT Test Name
CO-Oximetry: measurement of haemoglobin and oxygen gas exchange, including oxyhaemoglobin and O2 saturation. CO-Ox is also concerned with the determination of the so-called dyshaemoglobins- carboxyhaemoglobin and methaemoglobin
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Instruments A CO-Oximeter is usually connected to a blood gas analyser, where pO2 measurement is made. |
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Location within CDHB
Biochemistry, CHLabs. Radiometer ABL800 blood gas analyser including CO-Ox.
i-STAT meters can measure haematocrit and calculate haemoglobin but no CO-Oximetry is available.
Tests measured
In conjunction with pO2 measurement, haemoglobin, oxyhaemoglobin, deoxyhaemoglobin, carboxyhaemoglobin and methaemoglobin can be measured. There are many calculated parameters concerning oxygenation that can be of value- p50 (a point on an oxygen dissociation curve) and arterial/Alveolar tension gradients are two very useful calculations.
(Refer to the POCT Coordinator- click on the link below- for more information).
Sample and volume requirements
The ABL800 uses 175µL of heparinised arterial whole blood. Note that this is the actual sample volume- at least 300µL of arterial blood is required in a blood gas syringe.
Consumables
Refer to the POCT Coordinator for consumable requirements or other matters relating to CO-Oximetry.
Controls
Radiometer blood gas controls include CO-Ox components. Quality control samples are in use with all blood gas analysers in the CDHB.
Reference Range
All reference ranges can be found in the CHLabs test database. Click on the left hand menu link to Canterbury Health Laboratories home page, then click on "Tests".
Sources of Error
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Failure to mix the sample before analysis. This is extremely important with CO-Oximetry, where haemoglobin measurement is made by shattering the red cells using ultra-sound and then passing a beam of light through a thin film of the haemolysed blood. If the sample is not totally homogenous beforehand, an incorrect measurement will result. For more information on spectrophotometry, the process just described, click here.
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Blood clots in the sample
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Incorrect labelling,
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Insufficient sample.
Competencies
Where appropriate, competencies for CO-Oximetry are included in the general competency requirements for blood gas analysers. Contact the POCT Coordinator.
