Carboxyhaemoglobin

Keywords: COHb, Carbon monoxide

Specimen:1 mL blood in EDTA.
Method:

Haemoximetry.

Reference Interval:

Carboxyhaemoglobin 0.2-2.0% of total haemoglobin in normal blood; up to 8.5% in heavy smokers.

Application:

Investigation of possible carbon monoxide exposure and poisoning.

Interpretation:

In carbon monoxide poisoning, carboxyhaemoglobin levels provide an approximate guide to status.

Between 10-20%: headache and dyspnoea on exertion;
above 20%: confusion and irritability;
above 50%: unconsciousness, with death likely if exposure is prolonged;
above 70%: death is rapid.

Toxicity relates more to inhibition of mitochondrial cytochrome respiration than to interference with blood oxygen transport.

Reference:
Gorman D et al. Toxicology. 2003; 187(1): 25-38.