Carbon monoxide - National Poisons Information Service

National Poisons Information Service

A service commissioned by Public Health England




Members of the public

seeking specific

information on poisons

should contact:


In England and Wales:

NHS 111 - dial 111


In Scotland:

NHS 24 - dial 111


In N Ireland:

Contact your local GP or

pharmacist during

normal hours; click here

(www.gpoutofhours for GP

services Out-of-Hours.


In Republic of Ireland:

01 809 2166



professionals seeking

poisons information

should consult:

Carbon monoxide

Carbon monoxide (CO) exposure is a common form of poisoning in the UK. However, relatively little is known about its epidemiology. Since July 2015 NPIS has undertaken a project funded by the Gas Safety Trust to obtain more information, in particular confirmation of exposure, from healthcare professionals contacting the NPIS.


Data were collated from telephone enquiry data via the UK Poison Information Database and follow up questionnaires posted directly to all enquirers. For healthcare professionals accessing TOXBASE, a questionnaire was either emailed or posted directly to the user or their head of department if contact details were not submitted at the time of viewing TOXBASE.


During the first 18 months of the project there were 4,851 alerts submitted from TOXBASE and 419 calls to the NPIS telephone line regarding carbon monoxide. From these enquiries data were available for 1,227 patients.The majority of exposures (96.4%) were unintentional with only 44 patients exposed due to self-harm. Thirty-four exposures involved pregnant women (2.8%).


With respect to gender, 354 (28.9%) patients were male, 472 (38.5%) were female and gender was not specified in 401 (32.7%). Exposures comprised 859 adults (≥13 yrs) (70.0%) and 222 children (≤12 yrs) (18.1%). Age was undetermined in 146 exposures (11.9%).


The majority of unintentional exposures were associated with boiler failure (280; 24.7%) or an unspecified CO leak (144; 12.7%). In 192 (17.0%) cases of unintentional exposure, activation of a CO alarm prompted the patient to seek medical attention.


Carboxyhaemoglobin concentrations were available for 476 (38.8%) patients. This was measured from a blood test in 374 patients, from a breath test in 36 and pulse oximeter in 20, with the test type not reported for 46 patients. Overall, a positive correlation was reported between Poisoning Severity Score (PSS) and carboxyhaemoglobin concentration (Figure 1).


Carbon monoxide exposures associated with moderate, severe, or fatal outcomes were most commonly as a result of house fires, where other factors would likely have contributed to the severity of the observed clinical features. Excluding CO exposures secondary to house fires, unintentional CO exposures were most commonly of low severity (717 [58%] cases associated with no symptoms or mild symptoms only), with moderate severity recorded in 57 (5%) cases, severe symptoms in 18 (1.6%) cases and death in three (0.3%) cases.


Symptoms affecting the central nervous system were most common, with 492 (41.9%) patients reporting at least one of these. Gastrointestinal (15.7%) and cardiovascular (6.0%) symptoms were also commonly reported.


Figure 1. Relationship of carboxyhaemoglobin (%) at presentation to Poisoning Severity Score (PSS) (excluding house fires) (n=325)


The data presented here demonstrate the ability of the NPIS to collect valuable data on all aspects of CO poisoning from across the UK. With ongoing funding, the NPIS will continue to collect data to improve our understanding of the incidence and characteristics of CO poisoning in the UK.

Information from the NPIS Annual Report 2016/17.


| Reserach we undertake | Antidotes | Button batteries | Carbon monoxide | Cyanide | 2,4-dinitrophenol | Drugs of misuse | Electronic cigarettes | Glycols and methanol |Household products | Iron poisoning | Lead exposure | NSAIDs | Oral anticoagulants | Pesticides | Snake bite |