Short CommunicationThe effect of reducing the threshold for carbon monoxide validation of smoking abstinence - Evidence from the English Stop Smoking Services
Introduction
Measurement of biochemical markers of smoking (e.g. cotinine, carbon monoxide (CO)) can provide more accurate information on smoking status than self-report (Jarvis et al., 1987, SRNT Subcommittee on Biochemical Verification, 2002) and is recommended as standard in clinical trials and routine clinical practice (Department of Health, 2011, SRNT Subcommittee on Biochemical Verification, 2002, West et al., 2005). Biochemical markers are widely used in research and clinical practice (e.g. Department of Health, 2011, Fidler et al., 2011, Stapleton and Sutherland, 2011).
Although the nicotine metabolite cotinine is an optimal biomarker for discriminating smokers from non-smokers (Jarvis et al., 1987) expired-air CO also has good sensitivity (percent of non-smokers classified correctly) and specificity (percent of smokers classified correctly) (SRNT Subcommittee on Biochemical Verification, 2002). As it is cheaper and easier to use, provides immediate results and, unlike cotinine, can be used with people who are obtaining nicotine from nicotine replacement therapy, it is recommended for use in routine clinical practice (Department of Health, 2011, West et al., 2005).
The most commonly used CO threshold for validating smokers' self-reported abstinence is 10 parts per million (ppm), as for example defined by the Russell Standard (Clinical) (Department of Health, 2011, West et al., 2005).
It has been argued that the threshold should be reduced to increase specificity, and a number of lower thresholds have been proposed, ranging from 6.5 ppm (Deveci, Deveci, Acik, & Ozan, 2004) through 5 ppm (Low et al., 2004, Maclaren et al., 2010, Middleton and Morice, 2000, Secker-Walker et al., 1997) to 2-3 ppm (Cropsey et al., 2006, Javors et al., 2005). However, little information is available on the effect of different thresholds in practice.
The UK has the most extensive coverage of smoking cessation support clinics of any country and information is recorded on the clients attending the services, the support they receive and success rates as defined according to the Russell Standard (Department of Health, 2011). The available information provides a unique opportunity to assess the effect lower thresholds would have on success rates reported in clinical practice. Because no other objective measure of abstinence such as cotinine is being recorded in the services, it is not possible to calculate sensitivity and specificity, thus the aim of this study was to assess the impact of reducing the threshold for expired-air CO below 10 ppm on success rates in clinical practice.
Section snippets
Design
Data were obtained from QuitManager (North 51, Nottingham, UK), an online database system for recording information on client and intervention characteristics in accordance with the Department of Health's standard monitoring requirements (Department of Health, 2011). In 2011, there were about 150 stop smoking services across England, of which 58 Services used QuitManager and 47 agreed to share anonymized data for the current audit.
Participants
As defined by the Department of Health, a treatment episode is
Results
Out of all 315,718 completed treatment episodes, 110,558 (35.0%) reported abstinence and had a CO value of less than 10 ppm. The size of the difference for a single unit reduction increased with each reduction; initial single unit reductions made a very small difference, while the two lowest thresholds reduced the proportion of quit attempts defined as successful by about a quarter and by about a half, respectively (Table 1).
Logistic regressions showed weaker associations for all established
Discussion
We found evidence that a reduction of the threshold for expired-air CO concentration to validate abstinence would reduce success rates in clinical practice only marginally unless very low thresholds were introduced. An extreme reduction also weakened the association of quit success with previously established predictors, suggesting that more error would be introduced and accuracy reduced if such a threshold were used. Low thresholds may however be useful in specific situations in which the aim
Conclusion
A reduction of CO thresholds used to determine abstinence from smoking would have a very small effect on the success rates of attempts to stop smoking in clinical practice, unless thresholds were reduced drastically, which likely would decrease accuracy.
Role of funding sources
LSB's post is funded by the National Centre for Smoking Cessation and Training (NCSCT). IT's PhD studentship is funded by the Society for the Study of Addiction. LS is a member of the UK Centre for Tobacco Control Studies. RW is funded by Cancer Research UK and is a member of the UK Centre for Tobacco Control Studies. The funders had no role in the study design, collection, analyses or interpretation of the data, writing of the manuscript or the decision to submit the paper for publication.
Contributors
LSB designed the study, wrote the protocol and the final draft. IT conducted literature searches and statistical analyses and wrote an earlier draft of the manuscript. RW initiated the collaboration with the data provider, LS and RW contributed to the design and data analysis and revised the draft paper. All authors contributed to and have approved the final manuscript.
Conflict of interest
IT and LSB have no competing interests. LS has received honoraria for talk and travel expenses from manufacturers of medications for smoking cessation to attend meetings and workshops. RW has undertaken research and consultancy for companies that develop and manufacture smoking cessation medications. He also has a share of a patent in a novel nicotine delivery device.
References (15)
- et al.
The measurement of exhaled carbon monoxide in healthy smokers and non-smokers
Respiratory Medicine
(2004) - et al.
Breath carbon monoxide as an indication of smoking habit
Chest
(2000) - et al.
Exhaled carbon monoxide and urinary cotinine as measures of smoking in pregnancy
Addictive Behaviors
(1997) - et al.
The effectiveness of NHS smoking cessation services: A systematic review
Journal of Public Health (Oxford, England)
(2010) - et al.
What makes for an effective stop-smoking service?
Thorax
(2011) - et al.
Expired carbon monoxide levels in self-reported smokers and nonsmokers in prison
Nicotine & Tobacco Research
(2006) Local Stop smoking services. Service delivery and monitoring guidance 2011/12
(2011)
Cited by (25)
Cessation classification likelihood increases with higher expired-air carbon monoxide cutoffs: a meta-analysis
2021, Drug and Alcohol DependenceCitation Excerpt :The absolute proportion quit reported in a study likely influences future work and clinician adoption, without the consideration of how abstinence was determined. Comparing between categorical CO cutoffs, we found that studies using the highest cutoffs 9−10 ppm were 261% more likely to classify participants as quit than those using cutoffs 3−4 ppm, consistent with earlier studies that found a similar pattern of cessation classification when comparing between low and high CO cutoffs within their respective samples (Brose et al., 2013; Cropsey et al., 2008). However, we also observed significant differences between the middle cutoff categories (i.e., 5−6 and 7−8 ppm) versus the highest 9−10 ppm category—contrary to Brose et al. (2013).
Randomized Controlled Trial of a Smartphone Application as an Adjunct to Acceptance and Commitment Therapy for Smoking Cessation
2020, Behavior TherapyCitation Excerpt :Self-reported abstinence at posttreatment and 6-month follow-up was biochemically verified with a piCO Smokerlyzer carbon monoxide breath test monitor (Bedfont Scientific Ltd., 2017). In accordance with the manufacturer’s instructions and research on the expired-air carbon monoxide (CO) threshold for verifying smoking status (Brose, Tombor, Shahab, & West, 2013; Wee et al., 2015), a CO reading of > 10 parts per million disconfirmed self-reported abstinence. The longest assessment period—6-month follow-up—was the primary endpoint (Lee et al., 2015; van den Brand et al., 2017).
Want, need and habit as drivers of smoking behaviour: A preliminary analysis
2018, Addictive BehaviorsCitation Excerpt :At weeks 1 and 4, the participants reported whether they had smoked at all since the target quit date. Expired-air carbon monoxide concentration was used to confirm abstinence with a threshold of 10 parts per million (ppm) (Brose, Tombor, Shahab, & West 2013; Brose et al. 2011; Shahab 2014; West, Hajek, Stead, & Stapleton 2005). The threshold of 10 ppm was used because previous research has shown that this threshold provides very similar results to use of lower thresholds except when these are below 5 ppm at which point they appear to lose accuracy (Brose et al. 2013).
Should the threshold for expired-air carbon monoxide concentration as a means of verifying self-reported smoking abstinence be reduced in clinical treatment programmes? Evidence from a Malaysian smokers' clinic
2015, Addictive BehaviorsCitation Excerpt :An important question is what happens in routine clinical practice. In a large study involving the English stop smoking services, Brose, Tombor, Shahab, and West (2013) found that reducing the threshold to 5 ppm made very little difference to recorded abstinence rates after 4 weeks and reducing it below that appeared to increase misclassification rate. This was one study in one country.