Journal of International Oral Health

: 2018  |  Volume : 10  |  Issue : 2  |  Page : 71--76

Carbon monoxide breath analyzers and its role in tobacco cessation: A narrative review of literature

Ramprasad Vasthare1, Santhosh Kumar2, Lim Yan Ran Arron3,  
1 Department of Public Health Dentistry, Manipal College of Dental Sciences, Manipal, Udupi, Karnataka, India
2 Department of Periodontology, Manipal College of Dental Sciences, Manipal Academy of Higher Education, Manipal, Udupi, Karnataka, India
3 Former Dental Intern, Manipal College of Dental Sciences, Manipal Academy of Higher Education, Manipal, Udupi, Karnataka, India

Correspondence Address:
Dr. Ramprasad Vasthare
Department of Public Health Dentistry, Manipal College of Dental Sciences, Madhav Nagar, Manipal - 576 104, Udupi, Karnataka


This literature review was done to estimate the uses and effectiveness of carbon monoxide (CO) breath analyzers in identifying smokers and evaluating the role it can play in tobacco cessation programs. A web-based research on PubMed and Scopus from date of inception till 2016 was done for collecting data for the review. Our inquiry was limited to relevant articles with specific keywords. During the web search title and abstracts, 118 articles were screened for content and quality and 66 articles were selected to get an update on the desired information. As on date, there is enough evidence to prove the reasonably high sensitivity and specificity of CO analyzers in distinguishing smokers and nonsmokers. It also correlates well with smoking status. Its primary application is in validating smoking abstinence and as a motivational tool in smoking cessation programs. Due to its advantages over other biochemical assays, it is used in screening large population, in developing countries and in research. It can also detect pregnant women who are smokers and victims of passive tobacco exposure. However, it does possess limitations which have to be taken into account when using it. It can be concluded that CO analyzers are proven to have great potential and can be used as an adjunct in achieving the goal of combating tobacco addiction. It is cheap, noninvasive, gives immediate results, easy to use, and it can be self-administered by individuals. It should henceforth be considered as an invaluable tool for tobacco cessation programs.

How to cite this article:
Vasthare R, Kumar S, Arron LY. Carbon monoxide breath analyzers and its role in tobacco cessation: A narrative review of literature.J Int Oral Health 2018;10:71-76

How to cite this URL:
Vasthare R, Kumar S, Arron LY. Carbon monoxide breath analyzers and its role in tobacco cessation: A narrative review of literature. J Int Oral Health [serial online] 2018 [cited 2023 Dec 9 ];10:71-76
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Full Text


Tobacco smoking is one of the most common deleterious habits in the world. Based on the World Health Organization fact sheets, there are approximately 1 billion smokers with 7 million deaths due to tobacco use every year globally.[1] Tobacco smoke contains more than 4000 chemicals and around 40 carcinogens, including nicotine, tar, and several others. The “forgotten killer,” carbon monoxide (CO) detected in breath analyzers is not mentioned very often.[2],[3] Hence, this review article was planned with the aim of selecting the relevant literature with evaluation, comparison, and critical appraisal of the conclusions drawn from the various studies.

 Search Criteria

A web-based research on MEDLINE and Scopus from date of inception till 2016 was done for collecting data for the review. Keywords used for research were “carbon monoxide breath analyzer,” “carbon monoxide threshold level,” “carbon monoxide determination,” “smoking carbon monoxide breath test,” and “smoking cessation carbon monoxide breath test.” The included articles and references were published in between 1977 and 2016. A sharp focus to evaluate CO breath analyzers in detecting tobacco smoking and assisting in a smoking cessation program, inclusion and exclusion criteria based on the research question were used for selection of the articles. The inclusion criteria were of any studies that evaluate the effectiveness of CO breath analyzers of any brand in detecting tobacco smoking. Publications and studies which use the CO breath analyzers to measure and compare breath CO (BCO) levels of smokers and nonsmokers were also included. Any studies that use CO breath analyzers in tobacco cessation programs were added. Studies which compare CO breath analyzer with other biochemical measurements as smoking indicators were also included. Descriptive, cross-sectional, or experimental studies were all included in the review. Meanwhile, articles that discuss the use of CO analyzers and evaluation of BCO with respect to nontobacco-related fields were not included. Nonhuman studies were also excluded from the study.

All relevant chosen articles were organized in the order of publication date to follow the subject developments topic closely. The citations of related articles were also screened in case any data were missed out on search database. Sixty-six articles were selected and included. The results and subsequent conclusions were extracted and reviewed. No meta-analysis was done, in keeping with the nature of literature review.

 Article Selection and Major Findings

Sixty-two articles were included in the review and presented in [Table 1]. The significant findings and conclusions were extracted and grouped to compare the amount of available evidence for justifying the use of BCO analyzers in tobacco cessation.{Table 1}


Effectiveness in detecting tobacco smoking

Jarvis et al. and Wald et al. were among the earliest researchers who evaluated the expired air CO by CO analyzer and carboxyhemoglobin in venous blood of smokers since more than 35 years ago. They observed that the readings correlated well with each other and smoking increases the CO concentration in the body.[4],[5] Measurement of CO concentrations therefore provides an unbiased indication of smoking habit. Assessment of CO concentration is preferably done by the expired air rather than by analyzing the blood sample due to the noninvasiveness and simpler procedure.[4] This invariably set up the foundation principle for the use of CO breath analyzers to detect smoking habits. Jarvis et al.[4] among others concluded that the availability of reliable and low-cost CO analyzers should allow application in health care and health education settings.[5]

In a recent large-scale study involving 309 participants, Maclaren et al. reported a good agreement between self-reported tobacco smoking and BCO with more than 93% sensitivity and specificity when cutoffs of ≥7 ppm and ≥5 ppm are used in remote Australian Indigenous communities.[6] Deveci et al. assessed BCO levels of 322 participants and found 90% sensitivity and 83% specificity when a cutoff of 6.5 ppm was used.[7] Other studies reported similar high sensitivity and specificity when used to validate questionnaires or other biochemical measurements.[8],[9],[10],[11],[12],[13],[14],[15],[16]

In many studies, the CO concentration in exhaled breath of smokers is significantly higher than nonsmokers,[7],[9],[11],[15],[17],[18] but no definite cutoff has been defined.[6],[12],[15],[17],[18],[19],[20] Researchers have recommended or used variable cutoff as high as 10 ppm,[20] at 9 ppm,[10],[21],[22],[23] 8 ppm,[14],[17],[18],[19] 7 ppm,[24] 6 ppm,[9],[13],[18],[25],[26] 5 ppm,[11],[27],[28],[29] 4.5 ppm,[16] 4 ppm,[19] or even as low as 2–3 ppm,[12],[14],[17],[23] resulting in different but still reasonably high combination of sensitivity and specificity. However, it is frequently reported that CO analyzers have low ability to detect light or atypical smokers.[10],[14],[21],[23],[30],[31],[32] Nevertheless, CO breath analyzer is still a reasonably dependable tool in detecting habitual smokers by inevitable increase in CO concentration in their breath.

Relationship with smoking status

In spite of high air pollution levels, exhaled BCO levels still correlate well with the smoking status, number of cigarettes smoked per day and time since last smoke. Therefore, it was concluded that BCO analyzers provide a logical and immediate assessment of participants' current smoking status.[7],[11],[12],[13],[30],[32],[33],[34],[35],[36] Thus, BCO analyzers have the potential to be used as an adjunct in smoking control assessment in settings such as military or smoke-free policy in public.[11] Studies and experts believe that the CO breath test is an excellent gauge of plasma nicotine levels, severity of nicotine dependence, and the likelihood of cravings during abstinence.[37],[38],[39]

Comparison with other biochemical tests

The comparison had been drawn by Jarvis et al. and Wage et al. between CO analyzer and other biochemical tests. It was found that the concentration of cotinine measured in plasma, saliva, or urine had the highest sensitivity and specificity to detect smokers. In comparison, CO concentration in blood and expired air had relatively lower sensitivity than cotinine. Thiocyanate had the worst performance. The conclusion was that the smoking indicator of choice is cotinine due to its excellent precision, but CO measurement has sufficient accuracy to be used in most clinical applications. In addition, it is available at a much lower cost, provides immediate real-time results, and is noninvasive, simple and easy to use, therefore should be considered.

On the other hand, other reports suggested that cotinine remain superior, especially when testing sustained smoking abstinence with nonnicotine medication. This is due to the short half-life of expired CO. For smokers who had short-term abstinence which only happened hours before evaluation, their BCO levels might be low. BCO analyzer might fail to detect their smoking status, thereby exaggerating treatment success rate.[32],[40] Some researchers concluded from their studies that to distinguish smokers and nonsmokers, the results were better when CO analyzer was combine with one other biochemical indicator such as serum thiocyanate or saliva cotinine, which outperformed CO analyzer alone.[8],[27] The algorithm was also developed for this purpose.[23] Two other studies concluded that in normal dental practice, the authority of health-care profession itself would seem to increase the validity of self-reporting by patients, rendering biochemical verifications such as BCO needless.[31],[41]

Use in pregnant population

Studies done on pregnant population show that CO breath test is recommended over cotinine assay to measure of cigarette use.[19] However, a lower cutoff point of 4 ppm or 2–3 ppm is necessary to correctly identify pregnant smokers.[14],[19] Another study found that pregnant women and newborn end-tidal CO measured using CO analyzer is reported to correlate well with maternal smoking in a study. Therefore, it can also be used as a noninvasive means to estimate antenatal smoking exposure.[42],[43],[44],[45] This can be useful in smoking cessation programs directed at pregnant women because exposure to tobacco smoke is harmful to the fetus. The amount of CO in fetuses is referred to as percentage of fetal carboxyhemoglobin (%FCOHb). Breath analyzers can estimate %FCOHb and are used to discourage tobacco smoking in pregnant women.

Detection of passive smoking or environmental tobacco exposure

Besides, CO breath analyzers can also be used to detect exposure to passive smoking in nonsmokers, with the mean BCO level (ppm) after exposure to environmental tobacco smoke (ETS) for 9 h or more being higher than preexposure and those not exposed to it.[35],[46],[47]

In one study, Alzeidan et al. reported low effectiveness (32.5% sensitivity and 69.2% specificity) of BCO analyzer to detect ETS exposure among Saudi pregnant women. It was concluded in the study that BCO test is an ineffective tool in the given context.[48] However, we found that this is the only study included which used a rogue CO monitor called the BMC-2000 provided by Senko Co Ltd. It was discovered that the sensor in this CO monitor is for industrial use and therefore has an extremely high cross-sensitivity to hydrogen. This CO monitor confuses H2 for CO, and since H2 is a highly abundant gas in the human body due to malabsorption of sugars in food, this can produce false higher readings, causing erroneous results.[49] An independent report concluded that “BMC-2000 CO monitor should not be sold or used in the UK/EU for medical smoking cessation applications.”[50] That being the case, the result of this study should be taken with due caution.

Validating in smoking cessation programs

Smoking cessation programs require a valid and convenient way to monitor the smoking abstinence status to assess the effectiveness of the program.[20],[30],[45],[51],[52] When smokers feel pressure, their self-report, which is often used to validate abstinence may not be always reliable. Hence, measuring components or byproducts of inhaled cigarette smoke in the serum, saliva, or urine can be used to estimate smoking levels. For instance, cotinine (the major metabolite of nicotine [53]) assays, thiocyanate, nicotine, carboxyhemoglobin can be done. However, these tests are costly, time-consuming, invasive, and inconvenient, thus resulting in subject noncompliance.[6] In smokers who use nicotine replacement therapy as quitting assistance, cotinine measurement will also not be accurate to detect abstinence. This happens even in pregnancy as the physiologic changes render cotinine measurement inaccurate.[54] As BCO test does not possess the aforementioned disadvantages, it is a better alternative.

Cut off level: A cutoff level of 5 ppm on the CO breath monitor can be considered close to optimum to decide whether one is a smoker. In an ex-smoker, the amount of CO in exhaled breath decreases to normal levels such as nonsmokers.[12],[30] Therefore, smokers who claim to have stopped smoking can be instantly checked and validated.[6] Clinician can use CO breath analyzers as an objective clinical tool to spot addicted tobacco users, and then proceed to assess their addiction, educate, and motivate them to quit.[55] Smokers are also less inclined to lie when they report for follow-up if they know that their self-report will be validated by a BCO analyzer. The CO threshold of ≥10 ppm is the most commonly used for validating smokers' self-reported abstinence. Contrasting studies exist as to whether reducing the threshold has any effect on the success rate.[17],[20],[52],[56]

In contrary, some studies suggested that for abstinence to be evaluated more accurately, other biochemical methods are preferred because of disadvantages of BCO method, such as short half-life, various confounding factors, and lowered ability to detect atypical or light smokers.[32],[40]

Still, all the inherent advantages of CO breath analyzers such as relatively cheap cost, simple, portable, noninvasive, and ability to provide quick and immediate real-time results add to its great potential to be a tool in smoking cessation program.[8],[32],[43],[57]

Motivational tool in smoking cessation programs

A study in British Medical Journal compared three different antismoking interventions using a controlled trial. The group which received antismoking advice and demonstration of exhaled CO had the highest smoking cessation rate, outperforming control, group which received only advice and group which received advice plus offer of further help from a health visitor.[58] There is also extra incentive to motivate smoking cessation as it is a common knowledge that CO is a somewhat poisonous gas.[33],[57],[58]

CO in breath is a form biofeedback of the smokers' own body. Psychologically, it helps in a way that smokers feel their own body is being harmed by the gas and they can control the damage by stopping smoking. When smokers achieve abstinence and their expired BCO level decrease to normal range, this gives them a feeling of satisfaction and achievement, attaining a positive reinforcement effect psychologically. It can be used to help smokers with real determination to quit as it is easily self-administered and shows high patient compliance.

In other studies, researchers found that when advice from counselor was coupled with using CO analyzer results as biofeedback, the smokers were more influenced and more motivated to quit.[59],[60] BCO values were also effectively used in shaping smoking cessation for hard-to-treat participants.[61]

Use in research and epidemiological studies

BCO analyzers are tools suitable for both clinical and community-based studies to detect tobacco exposure and confirm reported abstinence.[30],[62],[63] For studies in developing countries, the low-cost and simple procedure of BCO analyzers should make it the first choice among various methods of biochemical assays. This is because factors other than validity and accuracy, such as monetary resource, time, personnel, and technical availability play an important role when research is to be done in these circumstances. The need for time-consuming, costly, and special technical laboratory ceases to be a concern. BCO analyzers can also be used in multilingual countries because of the simple instructions and procedure requiring minimal explanation.

Kumar et al. used CO breath analyzer as a tool to measure the BCO to make a comparison between cigarette and bidi smokers in India. They found that although the tobacco content in bidi is one-third of that in cigarette, BCO levels are higher in bidi smokers. Besides that, BCO levels were also used in research to measure smoking and vaporization of cannabis.[64] Another group of researchers used BCO levels to prove that water-pipe smoking was as harmful to health as cigarette smoking.[36]

In various epidemiological studies, particularly in cultures where women have moral, social and economic constraints, smoking habits may be underreported.[21],[22],[25],[65] Using objective biochemical assays to detect smoking on the other hand, provide researchers more accurate and less biased results. Comparing the available biochemical assays, BCO is more cost-effective, fast, practical, and acceptable to the public than the others, proving its worth as the first choice, especially in large population. Expired alveolar CO is therefore often used as a validation tool for detecting smoking in various researches.

Another added advantage is that for studies which assess the effects of smoking, the ability to dichotomously separate smokers and nonsmokers using biochemical indicators gives greater power and confidence than using self-reporting. Therefore, in clinical studies, where recent smoking status has an impact on the outcome, CO analyzers can also be applied as an objective assessment, with a proposed higher cutoff of 10 ppm or 12 ppm CO.[15],[66]

Disadvantages of breath carbon monoxide analyzers

However, in different populations of the world and in different ethnicity, the optimum BCO cutoff to distinguish smokers and nonsmokers is still being investigated.[6],[17],[18],[19] We also have to recognize that BCO level has a colossal list of confounding factors. Smoking pattern,[67] type of tobacco, brand, and tobacco content all affect the BCO level. Confounding factors such as environmental exposure,[7],[14],[30] cannabis [6],[19] or alcohol abuse, physical activity after smoking,[9] diet,[15] and various pulmonary diseases demand careful use in complex situations. Some reported that even ovarian cycle,[68] gender,[69] and time of the day [15] compromise the consistency in value.

To counter the drawback, the cutoff level should be individualized for the intended purpose. Confounding factors should be identified and taken into account. Combining it with one other biochemical assay can help detect light or atypical smokers. Currently, companies are also coming up with innovative products. In conclusion, after considering both the positive and negative, CO analyzers have tremendous benefits that outweigh its disadvantages. It is a sufficiently effective tool to be used most smoking cessation programs and therefore should be considered for use in war against tobacco.


In order for the literature review to be as inclusive as possible, the review included a large amount of information from over three decades. While the quality of studies included was high, there might be differences in guidelines for designing, analyzing, and reporting the clinical research, due to the wide span of time considered. Therefore, some of the research studies may be considered outdated or even primitive but is nevertheless important in our view as it is the foundation of BCO analyzers usage.

The CO breath analyzers have sometimes proved ineffective to detect environmental tobacco exposure in patients who are asked to self-report the use of tobacco or who have a light usage of tobacco.

There are no significant controversies or conflicts of interests with the various manufacturers of BCO analyzers as we have not mentioned, compared, or attempted to promote any particular brand of breath analyzers.

When a breath analyzer is used to detect smoking status or abstinence of smoking, it tends to miss out on the light smokers as well as in those with short-term abstinence due to CO's short half-life in the respiratory system.

Future research directions

A significant percentage of pregnant women are exposed to ETS. Exposure to ETS to nonsmoking pregnant women has harmful effects on pregnancy outcomes comparable to those observed in actively smoking pregnant women, including stillbirth, congenital malformations, low birth weight, intrauterine growth retardation, sudden infant death syndrome, miscarriage, and preterm delivery. This area is a priority area for the efficient use of breath analyzersFuture studies should focus on refining the cutoff level for use in different clinical situations, as the review of literature noticed a lack of consensus among researchers on the cutoff levels to be used. The results can then be used to produce reliable guidelines, to improve the confidence of using CO breath analyzersThird, factors that affect BCO level should be identified through control studies, and then, the definite relation and function of the factors to the BCO should also be determinedAntenatal setting represents a great opportunity for health professionals to raise awareness and promote use of use breath analyzers as a health promotion and monitoring toolA meta-analysis of the studies available is also suggested to bring out the finer aspects and for a comprehensive address on the related aspects, which will further highlight the effectiveness of BCO analyzers.


Cigarette smoking kills millions of people each year. CO breath analyzers have been proven to be very useful to assess smoking status. Review of the literature concluded that CO analyzers have great potential to be used as an adjunct in achieving the goal of combating tobacco addiction. It is cheap, noninvasive, gives immediate results, easy to use, and it can be self-administered by individuals. Its main application is in smoking cessation programs. Due to its advantages over other biochemical assays, it is also used in screening large population, developing countries, validating smoking abstinence, and research. Even though it possesses certain limitations which have to be taken into account, the use of CO breath analyzers should be further encouraged in appropriate situations to increase awareness on the harmful effects of CO (and hence tobacco) on health, which emphasizes the importance of smoking cessation. All in all, BCO analyzers with its numerous advantages, have the potential to be an invaluable tool to have for any tobacco cessation programs and clinics with a serious intent to reduce tobacco consumption and eventual cessation of tobacco use.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.


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