CKS is no longer commissioned by the National Institute for Health and Clinical Excellence (NICE). NICE remains committed to providing a replacement service for CKS and is currently reviewing its options. In the meantime, although CKS content is now not being maintained, it still remains relevant and will continue to be made available. CKS content was generated under a programme of topic creation and update. To check if the topic you are viewing is current or out of date, please refer to the topic publication details by clicking on the 'How up-to-date is this topic?' link in the left hand menu on individual topic pages.
Carbon monoxide poisoning - Management
How do I interpret investigations into carbon monoxide poisoning?
- In people with suspected carbon monoxide poisoning the diagnosis is based on identifying a source of carbon monoxide emissions and measuring carboxyhaemoglobin levels.
- A definite diagnosis is not always possible because:
- Identifying a source of carbon monoxide exposure supports the diagnosis, but not finding a source does not exclude it. Sources of carbon monoxide poisoning may be intermittent making them difficult to detect.
- Identifying an abnormally raised carboxyhaemoglobin level confirms the diagnosis, but finding a normal level does not exclude it. Even a relatively short delay between exposure and taking the test can result in a normal carboxyhaemoglobin level because levels fall by half every 2 to 5 hours after exposure. Normal carboxyhaemoglobin levels are:
- Less than 1–2% for people who live away from urban areas and who do not smoke.
- Up to 5% for people who smoke up to 20 cigarettes a day, people living in urban areas who do not smoke, and pregnant women.
- Up to 13% for heavy smokers has been recorded.
- Diagnose:
- Possible carbon monoxide poisoning if:
- The person has symptoms of carbon monoxide poisoning, but
- A source of carbon monoxide emissions cannot be identified, and
- Carboxyhaemoglobin levels are normal.
- Probable carbon monoxide poisoning if:
- The person has symptoms of carbon monoxide poisoning, and
- A source of carbon monoxide emissions was identified, but
- Carboxyhaemoglobin levels are within normal range.
- Confirmed carbon monoxide poisoning if:
- The person has symptoms of carbon monoxide poisoning, and
- A source of carbon monoxide emissions was identified, and
- Carboxyhaemoglobin levels are abnormally raised.
© NHS Institute for Innovation and Improvement