As mentioned elsewhere in this blog, COHb (carboxyhaemoglobin) is NOT a stable compound. It has a half-life of around four hours when you breathe 'clean air (i.e. 21% O2), which shortens the higher the concentration of oxygen you breathe.
So if someone is tested for COHb levels some hours after exposure, those levels will have FALLEN.
COHb testing is like any other clinical investigation- it must be used judiciously and interpreted in light of other clinical findings. As always, an accurate history is often more inportant than getting a high COHb reading. If someone has symptoms suggestive of exposure, and if those symptoms are worse when they are inside their house, those findings are much more important than getting them to score on a CO-oximeter or a breath meter.
