Elsevier

Addictive Behaviors

Volume 38, Issue 10, October 2013, Pages 2529-2531
Addictive Behaviors

Short Communication
The effect of reducing the threshold for carbon monoxide validation of smoking abstinence - Evidence from the English Stop Smoking Services

https://doi.org/10.1016/j.addbeh.2013.04.006Get rights and content

Highlights

  • Carbon monoxide concentration in expired-air is used to verify smoking abstinence.

  • Current standards define < 10 parts per million as threshold for successful quitting.

  • A reduction of this threshold has been suggested.

  • Data from > 300,000 cases used to assess effect of reduction on success rates.

  • Effect minimal unless threshold reduced dramatically which would increase error.

Abstract

Introduction

The most commonly used threshold of expired-air carbon monoxide (CO) concentration to validate self-reported smoking abstinence is < 10 parts per million (ppm). It has been proposed to reduce this threshold. This study examined what effect a reduction would have on short-term success rates in clinical practice.

Methods

A total of 315,718 quit attempts supported by English NHS Stop Smoking Services were included in the analysis. The proportion of 4-week quits as determined by the Russell standard (< 10 ppm) that also met lower thresholds was calculated for each unit change from < 9 ppm to < 2 ppm. Additionally, associations of established predictors with outcome were assessed in logistic regressions for selected thresholds.

Results

At < 10 ppm, 35% of quit attempts were regarded as successful. Differences for a single unit reduction increased with each reduction; small reductions had very little impact (e.g. < 8 ppm: 34.7% success), but at < 3 ppm, only 26.3% would still be regarded as successful. With the threshold reduced to < 3 ppm established predictors of cessation showed a weaker association with outcome than with the threshold at < 10 ppm suggesting an increase in error of outcome measurement.

Conclusions

Reducing the threshold for expired-air CO concentration to validate abstinence would have a minimal effect on success rates unless the threshold were reduced substantially which would likely increase error of measurement.

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)

There are more references available in the full text version of this article.

Cited by (25)

  • Cessation classification likelihood increases with higher expired-air carbon monoxide cutoffs: a meta-analysis

    2021, Drug and Alcohol Dependence
    Citation Excerpt :

    More recently, research has supported lowering the threshold to 6 ppm and potentially to as low as 3 ppm as a means of increasing specificity (Cropsey et al., 2006 2014; Deveci et al., 2004; Javors et al., 2005; Low et al., 2004; MacLaren et al., 2010; Perkins et al., 2013). Single sample non-randomized studies assessing the impact of reducing the CO threshold on cessation prevalence found mixed results, depending on which CO cutoff was employed (Brose et al., 2013; Cropsey et al., 2008). For example, Cropsey et al. (2008) found that the prevalence of cessation doubled when comparing a cutoff of 3 ppm versus the standard 10 ppm (18.4% vs. 37.2% at end of treatment).

  • Randomized Controlled Trial of a Smartphone Application as an Adjunct to Acceptance and Commitment Therapy for Smoking Cessation

    2020, Behavior Therapy
    Citation 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).

  • Lessons learned from unsuccessful use of personal carbon monoxide monitors to remotely assess abstinence in a pragmatic trial of a smartphone stop smoking app – A secondary analysis

    2019, Addictive Behaviors Reports
    Citation Excerpt :

    Remote assessment of heart rate variability through a smartphone camera has not been validated yet, but it could offer another, potential cost-effective and convenient method (Harte & Meston, 2014; Heathers, 2013; Peng et al., 2015). Assessment of carbon monoxide (CO) in the exhaled breath has been among the most commonly used methods in many cessation programmes (Goldstein et al., 2018; West et al., 2010), with readings lower than 10 particles per million (ppm) commonly accepted as confirmation of abstinence (Brose et al., 2013; West et al., 2005), but with lower cut-off levels of 5 ppm suggested more recently (Perkins, Karelitz, & Jao, 2013). CO testing has important advantages over the other methods as it is non-invasive, and insensitive to concurrent use of nicotine products or e-cigarettes, although its temporal applicability is limited due to rapid elimination of CO from the body (Benowitz et al., 2002; Goldstein et al., 2018).

  • 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 Behaviors
    Citation Excerpt :

    Age was a consistent predictor of success across the different CO thresholds at 1-, 3- and 6-month follow-up. The current findings confirm the findings of Brose et al. (2013) in suggesting that a threshold of 10 ppm is acceptable in clinical situations. The current findings provide a fair degree of confidence that a threshold of 10 ppm is appropriate internationally for determining predictors.

View all citing articles on Scopus
View full text