International Journal of Psychiatry in Clinical Practice, 2010; 14: 282–286
ORIGINAL ARTICLE
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Validity of the self-reported smoking status of schizophrenia patients, taking gender-related differences into consideration
TAKEAKI TAKEUCHI1,2, MUTSUHIRO NAKAO1,2, YASUKO SHINOZAKI1,3 & EIJI YANO1 1Department
of Hygiene and Public Health, Teikyo University School of Medicine, Tokyo, Japan, 2Division of Psychosomatic Medicine, Teikyo University Hospital, Tokyo, Japan, and 3Division of Psychiatry, Kichijyoji Hospital, Tokyo, Japan
Abstract Objective. It is unclear whether self-reported smoking status reflects the true smoking status in schizophrenia patients. This study aims to evaluate the consistency in smoking status in schizophrenia patients, as determined using self-reported questionnaires and objective measurements, while considering gender-related differences. Methods. The study involved 158 Japanese schizophrenia patients (79 men and 79 women), who were diagnosed according to DSM-IV-TR criteria. The patients answered questions about their smoking status and daily cigarette consumption. The carbon monoxide (CO) level in the expired air was measured to confirm the self-reported answers. We descriptively analysed the data and assessed the proportion of results showing consistency between the self-reported smoking status and measured CO levels. Results. The self-reported smoking status was consistent with the objective measurement results in both genders. Among the various cut-off CO levels considered, 7 ppm was found to be the optimal level in both men and women. Conclusions. Our study showed that self-reporting is a reliable method for evaluating the smoking status of schizophrenia patients, regardless of gender. However, for precise assessment on the basis of CO levels in expired air, lower cut-off points may be better than the recommended ones. Key Words: Gender, schizophrenia, self-reporting, smoking, validity
Introduction It is reasonable to advise schizophrenia patients to quit smoking for health reasons, because patients who smoke regularly are at a higher risk of developing coronary heart diseases and stroke than the general population [1]. Further, ischemic heart disease is the most common cause of death among schizophrenia patients [2]. In clinical settings, psychiatrists usually determine the smoking status of patients through interviews or self-reported questionnaires filled out by the patients. Although Murray et al. reported that the self-reported smoking status is highly consistent with the smoking status determined by objective measurements in a non patient group [3], the self-reported smoking status is maybe more likely to be erroneous in schizophrenia patients because the patients’ responses largely
depend on their cognitive and/or mental condition [4]. However, to our knowledge, no study thus far has examined the accuracy of the self-reported smoking status of schizophrenia patients. In addition to the effects of schizophrenia, the basic and sensitive issue of gender-related differences should be considered when assessing the consistency between the self-reported smoking status and the true smoking status determined using biological markers [5,6]. The purpose of the present study is to compare the smoking status determined through self-reported questionnaires and objective measurements in schizophrenia patients, considering gender-related differences. In order to determine the validity of the self-reported smoking status, we monitored the carbon monoxide (CO) level in expired air.
Correspondence: Takeaki Takeuchi, MD, MPH, PhD, Department of Hygiene and Public Health, Teikyo University School of Medicine, 2-11-1 Kaga, Itabashi, Tokyo 173-8605, Japan. Tel: 81 3 3964 1211, ext. 2166. Fax: 81 3 3964 1058. E-mail: [email protected] (Received 24 July 2009 ; accepted 16 June 2010 ) ISSN 1365-1501 print/ISSN 1471-1788 online © 2010 Informa Healthcare DOI: 10.3109/13651501.2010.505342
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Self-reported smoking in schizophrenia
283
Materials and methods
Statistical analyses
Participants
First, the characteristics of the schizophrenia patients were descriptively analysed and compared between men and women. Second, to verify the relationship between self-reported smoking (smoking status as dichotomous values) and the CO level in expired air in our study, Spearman’s correlation analyses were performed in men and women, respectively. Then we compared those values to the values obtained from a previous study (correlation coefficient 0.71, P 0.01) [3] to assess the validity of the questionnaire. Third, to determine the optimal cut-off CO level in schizophrenia patients, the proportion of results in which the self-reported smoking status corresponded to the CO levels was analysed by using various cutoff levels. Further, to estimate the proportion of consistent results, we considered the self-reported smoking status as a fixed variable (assuming subjective report is trustable). We also calculated the proportion of “concordant patients”, that is, the number of self-reported smokers whose CO levels exceeded the cut-off level and self-reported non-smokers whose CO levels were below the cut-off level. The CO level that corresponded to the highest percentage of overlap was regarded as the optimal cut-off point [8]. Statistical analyses were conducted using STATA version 8.0 (StataCorp, College Station, TX), and P values of 0.05 in two-tailed tests were regarded as statistically significant.
We recruited 158 Japanese patients with schizophrenia (79 men and 79 women) from a psychiatric clinic located in a suburban area of Tokyo. The following patients were selected: (1) those who were treated by the physicians in charge between November 2007 and April 2008; (2) those who were diagnosed with schizophrenia as per the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision (DSM-IV-TR), during this period; (3) those with a stable medical condition (chlorpromazineequivalent dose, 1062.5 mg) and who had been on a constant drug regimen for more than 1 month; (4) those with no respiratory diseases that increase the CO levels, such as chronic obstructive pulmonary disease (COPD); and (5) those who agreed to participate in this study by signing the written informed consent form that described in detail the purpose and nature of the study and the risks associated with all the procedures. All the patients were hospitalized and isolated from environments that would increase the CO levels in expired air. None of the patients had regular jobs because their condition rendered them unable to lead normal social lives. Twenty-seven patients (17.1%) had a family history of schizophrenia, with the condition having affected third-degree relatives. This study was performed in accordance with the World Medical Association Declaration of Helsinki, and the protocol was approved by the Institutional Review Board of Teikyo University School of Medicine. Self-reported smoking status and CO measurement The patients were required to answer questions about their smoking status (classifying themselves as current smokers, former smokers, or non-smokers) and daily cigarette consumption, and the Fagerström test for nicotine dependence (FTND) was administered. CO levels in the expired air were measured with the Micro Smokerlyzer system (Bedfont Technical Instruments Ltd., Kent, UK); a psychiatrist proficient in using the equipment performed the measurements. The recommended cut-off level regarded as non smoking is less than 10 ppm [7]. The participants were instructed to inhale and hold their breath for 20 s and then exhale into the instrument. The endtidal CO reading in the expired air was measured during two trials, and the average of the two readings was used for the subsequent analyses. The average time intervals (meanSD) between the time they measured their CO levels and that of the last cigarette they smoked were 5.15.6 min in men and 4.0 8.2 min in women, respectively.
Results The patient characteristics are shown in Table I. In both men and women, 13 out of 79 people (16.5%) in both sexes smoked their first cigarette within 5 min of waking up. The number of self-reported current smokers was higher among the men than among the women (41 vs. 36%, P 0.05), and the mean daily cigarette consumption among smokers was also higher in the men than in the women (17.4 vs. 8.2, P 0.05). The age of the subjects, duration of disease, education level, FTND scores, and CO levels did not differ significantly between sexes. Correlation coefficients between smoking status and CO levels were both 0.76, p 0.01 in men and women, which were higher than that of the previous study [3]. Table II shows the percentage of results in which the self-reported smoking status was consistent with various CO cut-off levels. On the whole, the selfreported smoking status showed high consistency with the various cut-off levels of CO in the expired air. Of the various cut-off CO levels tested, 7 ppm was found to be the optimum level (with the lowest number of misclassifications) in both men and women. In men, the highest proportion of concordance
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Table I. Comparison of patient characteristics between men and women (N 158).
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Number (%), otherwise specified
Age: mean SD, years Duration of schizophrenia: mean SD, years 10 10–19 20–29 30 Educational level: mean SD, years Middle school High school Vocational school/2-year college University/higher Self-reported smoking data Smoking status Current Former smoker Non-smoker Daily consumption of cigarettes: mean SD FTND score: mean SD First cigarette after waking up, minutes 5 6–30 31–60 60 Difficulty of refraining from smoking, positive answer Hated to give up morning cigarettes, positive answer Daily cigarette consumption 10 11–20 21–30 31 Frequently smoking after waking up, positive answer Smoking in bed in spite of sickness, positive answer Carbon monoxide intake in terms of number of cigarettes: mean SD, ppm Smoking status Current Former smoker Non-smoker
Men (n 79)
Women (n 79)
P value
53.2 14.9 28.5 15.4 10 (12.6) 13 (16.5) 18 (22.8) 38 (48.1) 12.3 2.7 23 (29.1) 23 (29.1) 16 (20.3) 17 (21.5)
56.1 15.5 28.0 11.1 9 (11.4) 18 (22.8) 12 (15.2) 40 (50.6) 12.2 2.2 18 (22.8) 33 (41.8) 18 (22.8) 10 (12.6)
NS NS NS
32 (40.5) 22 (27.9) 25 (31.6) 17.4 28.9 2.2 3.1
28 (35.5) 5 (6.3) 46 (58.2) 8.2 11.9 1.9 2.8
0.05
13 13 1 52 13 20
(16.5) (16.5) (1.2) (65.8) (16.5) (25.3)
13 12 2 52 14 15
(16.5) (15.2) (2.5) (65.8) (17.7) (19.0)
NS NS
0.05 NS NS
NS NS
55 (69.6) 11 (13.9) 8 (10.1) 5 (6.3) 17 (21.5) 19 (24.1) 10.0 9.9
61 (77.2) 10 (12.7) 8 (10.1) 0 (0.0) 15 (19.0) 14 (17.7) 8.6 9.2
NS
NS NS NS
19.1 10.2 4.0 1.2 3.7 1.0
18.0 10.1 3.8 0.8 3.5 1.1
NS NS NS
FTND, Fagerström Test for Nicotine Dependence; SD, standard deviation. Two-tailed t-tests were used to compare the mean differences. For categorical variables, Fisher’s exact tests or proportion tests were used.
(96.2%) was found at CO levels of 7 and 8 ppm, followed by 9 ppm (94.9%). In women, the highest proportion of concordance (94.9%) was found at levels of 7 ppm, followed by 6, 8, 9, and 10 ppm (93.7%). After defining 7 ppm as the cut-off level of CO in expired air, comparison of the self-reported smoking status and CO levels revealed that seven people were misclassified. Among men, misclassification occurred only in the self-reported smokers with low CO levels (n 3, 3.8%). Further, among the three men who were misclassified, the mean daily cigarette consumption was 5.3 (range, 5–6 cigarettes per day) and the mean CO concentration was 5.3 ppm (range, 4–6 ppm). Among women, misclassification occurred in both the self-reported smokers with low CO levels (n 3, 3.8%) and the self-reported non-smokers with
high CO levels (n 1, 1.3%). Among the three female smokers with low CO levels, the mean daily cigarette consumption was 6.3 (range, 3–10 cigarettes per day) and the mean CO concentration was 5.3 ppm (range, 3–5 ppm). Among the female non-smokers with high CO levels, the daily consumption was 0 cigarettes and the CO concentration was 8 ppm. Discussion For decades, many studies have been conducted to determine how aware schizophrenia patients are of their smoking status. However, no study has focused on the validity of the self-reported smoking status in schizophrenia patients while taking into account gender-related differences. The results of the present
Self-reported smoking in schizophrenia
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Table II. Gender-wise comparison of the consistency in the smoking status assessed with a self-reported questionnaire and each CO cut-off level (N 158). Percentage consistently classified Men (n 79)
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Carbon monoxide cut-off levels 4 ppm 5 ppm 6 ppm 7 ppm 8 ppm 9 ppm 10 ppm 11 ppm 12 ppm 13 ppm
Women (n 79)
Reported smokers
Reported non-smokers
Total
Reported smokers
100.0 96.9 96.9 90.6 90.6 87.5 84.4 81.3 78.1 71.9
44.7 74.5 89.4 100.0 100.0 100.0 100.0 100.0 100.0 100.0
67.1 83.5 92.4 96.2 96.2 94.9 93.7 92.4 91.4 88.6
92.9 92.9 89.3 89.3 85.7 85.7 82.1 75.0 75.0 67.9
Reported non-smokers 56.9 86.3 96.1 98.0 98.0 98.0 100.0 100.0 100.0 100.0
Total 69.6 88.6 93.7 94.9 93.7 93.7 93.7 91.1 91.1 88.6
Note: To estimate the proportion of consistent results, we considered the self-reported smoking status as a fixed variable. We calculated the percentage of overlaps between self-reported smokers with high CO levels and self-reported non-smokers with low CO levels at specific cut-off points. The total was calculated as the total percentage of people who were accurately classified by both the self-reported questionnaires and CO measurements. Values greater than or equal to the listed cut-off values were considered indicative of smoking, as defined above.
study revealed that: (1) self-reporting is a reliable method for evaluating the smoking status of schizophrenia patients, regardless of gender; (2) for precise assessment of CO levels in expired air among schizophrenia patients, 7 ppm is a better cut-off level than the usual level of 10 ppm [8–10]; and (3) according to the responses in the self-reported questionnaires, male patients tended to smoke more cigarettes than female patients, but no gender-related differences were apparent in terms of the FTND or CO levels. Self-reporting by schizophrenia patients provided an accurate reflection of their smoking status, although some misclassifications occurred because of trade-off. The mean daily cigarette consumption was found to be relatively low among self-reported smokers with low CO levels (5.3 in men and 6.3 in women). One self-reported female non-smoker had a relatively low CO level of 8 ppm. Our second finding of lower cutoff CO levels being optimal seems interesting. It is widely accepted that hydrocarbons associated with cigarette smoking induce hepatic enzymes and therefore reduce the plasma concentrations of antipsychotics [11]. Although opposing theory that increased antipsychotics reduce hydrocarbons or cigarette smoking has not yet been proved, there could be the possibility. With regard to our third finding, previous studies have reported gender-related differences in the smoking habits of schizophrenia patients: the daily cigarette consumption is higher in men than in women [12]. However, we did not find any significant gender-related differences in the FTND scores and CO levels. Because of the small sample size of this study, our results may not provide a strong conclusion. But as a possible mechanism, CYP1A2 activity
may induce faster nicotine clearance in male smokers than in female smokers, thus buffering the increment in the FTND scores and CO levels [11,13]. Several limitations of this study should be taken into consideration. First, the sample size was relatively small, and all patients were selected from the same hospital. Our study, however, was conducted in a clinical setting, and the patients were diagnosed with schizophrenia as per the DSM-IV criteria; therefore, the diagnosis itself was accurate. Second, the patients did not maintain constant time intervals between cigarettes smoked. However, our CO measurements were conducted after the lunch period at the hospital, when most smokers smoke. Since CO measurements should be performed within 6–9 h of smoking in order to achieve an accurate assessment [14], all measurements in our study can be considered sufficiently accurate. Third, the wide SD of the daily consumption of cigarettes indicated that the distribution might have some outliers. However, our analyses excepting outliers (two outliers in men) did not change our results. Finally, the true smoking status should have been evaluated by measuring biochemical markers such as cotinine or thiocyanate. However, Murray et al. reported that the cotinine and CO levels are both reliable measures [3]. Moreover, all our study participants were inpatients at our hospital and were not exposed to any major CO source like vehicle exhaust or burning coal. Moreover, compared to the conventional biochemical markers like cotinine, it is more practical to measure the CO levels in expired air for evaluating the smoking status in clinical settings. In addition to those, CO analysis costs less than $1 per sample, while cotinine analysis costs $20 per sample [15]. Finally,
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we attempted to determine that a cut-off carbon monoxide value is based on the fact that self-reported responses are accurate. Although we tried to establish the robust condition of self-report accuracy, it was not sufficient enough. Thus, despite the abovementioned limitations, our study conclusively revealed that self-reporting is a useful method for evaluating the smoking status of schizophrenia patients. Further, when psychiatrists or medical professionals use CO levels in expired air for precise assessment of the smoking status, using lower cut-off points than the recommended ones may increase the accuracy of the data.
[2]
[3]
[4]
[5]
[6] [7]
Key points
• Self-reporting is a reliable method for evaluating •
•
the smoking status among schizophrenia patients, regardless of gender For precise assessment of CO levels in expired air among schizophrenia patients, 7 ppm seems to be a better cut-off level than the recommended level of 10 ppm According to the responses in the self-reported questionnaires, men tended to smoke more cigarettes than women, but no gender-related differences were observed in terms of the FTND scores or CO levels
Acknowledgement
[8]
[9]
[10]
[11]
None. [12]
Statement of interest None of the authors have any conflict of interests to declare.
References [1] McCreadie RG, Scottish Schizophrenia Lifestyle Group. Diet, smoking and cardiovascular risk in people with
[13]
[14]
[15]
schizophrenia: Descriptive study. Br J Psychiatry 2003;183: 534–9. Lawrence D, Holma D, Jablensky A, editors. Preventable physical illness in people with mental illness. Perth: University of Western Australia Press; 2001. Murray RP, Connett JE, Lauger GG, Voelker HT. Error in smoking measures: Effects of intervention on relations of cotinine and carbon monoxide to self-reported smoking. Am J Public Health 1993;83:1251–7. Keefe RS, Fenton WS. How should DSM-V criteria for schizophrenia include cognitive impairment? Schizophr Bull 2007;33:912–20. Yano E. Japanese spousal smoking study revisited: How a tobacco industry funded paper reached erroneous conclusions. Tob Control 2005;14:227–33. Kaplan HI, Sadock BJ, editors. Synopsis of psychiatry, 10th ed. Philadephia, PA: Lippincott Williams & Wilkins; 2007. Hajiro T, Nishimura K, Tsukino M, Ikeda A, Koyama H, Izumi T. Comparison of discriminative properties among disease-specific questionnaires for measuring health-related quality of life in patients with chronic obstructive pulmonary disease. Am J Respir Crit Care Med 1998;157:785–90. Huang CL, Lin HH, Wang HH. Evaluating screening performances of the Fagerstrom tolerance questionnaire, the Fagerstrom test for nicotine dependence and the heavy smoking index among Taiwanese male smokers. J Clin Nurs 2008;17:884–90. Gonzales D, Rennard SI, Nides M, Oncken C, Azoulay S, Billing CB, et al. Varenicline, an alpha4beta2 nicotinic acetylcholine receptor partial agonist, vs sustained-release bupropion and placebo for smoking cessation: A randomized controlled trial. J Am Med Assoc 2006;296:47–55. Nides M, Oncken C, Gonzales D, Rennard S, Watsky EJ, Anziano R, et al. Smoking cessation with varenicline, a selective alpha4beta2 nicotinic receptor partial agonist: Results from a 7-week, randomized, placebo- and bupropioncontrolled trial with 1-year follow-up. Arch Intern Med 2006; 166:1561–8. Ng W, Uchida H, Ismail Z, Mamo DC, Rajji TK, Remington G, et al. Clozapine exposure and the impact of smoking and gender: A population pharmacokinetic study. Ther Drug Monit 2009;31:360–6. Leung A, Chue P. Sex differences in schizophrenia, a review of the literature. Acta Psychiatr Scand Suppl 2000;401:3–38. Faber MS, Fuhr U. Time response of cytochrome P450 1A2 activity on cessation of heavy smoking. Clin Pharmacol Ther 2004;76:178–84. Jatlow P, Toll BA, Leary V, Krishnan-Sarin S, O’Malley SS. Comparison of expired carbon monoxide and plasma cotinine as markers of cigarette abstinence. Drug Alcohol Depend 2008;98:203–9. Patrick DL, Cheadle A, Thopson DC, Diehr P, Koepsell T, Kinne S. The validity of self-reported smoking: A review and meta-analysis. Am J Public Health 1994;84:1086–93.
ORIGINAL ARTICLE
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Validity of the self-reported smoking status of schizophrenia patients, taking gender-related differences into consideration
TAKEAKI TAKEUCHI1,2, MUTSUHIRO NAKAO1,2, YASUKO SHINOZAKI1,3 & EIJI YANO1 1Department
of Hygiene and Public Health, Teikyo University School of Medicine, Tokyo, Japan, 2Division of Psychosomatic Medicine, Teikyo University Hospital, Tokyo, Japan, and 3Division of Psychiatry, Kichijyoji Hospital, Tokyo, Japan
Abstract Objective. It is unclear whether self-reported smoking status reflects the true smoking status in schizophrenia patients. This study aims to evaluate the consistency in smoking status in schizophrenia patients, as determined using self-reported questionnaires and objective measurements, while considering gender-related differences. Methods. The study involved 158 Japanese schizophrenia patients (79 men and 79 women), who were diagnosed according to DSM-IV-TR criteria. The patients answered questions about their smoking status and daily cigarette consumption. The carbon monoxide (CO) level in the expired air was measured to confirm the self-reported answers. We descriptively analysed the data and assessed the proportion of results showing consistency between the self-reported smoking status and measured CO levels. Results. The self-reported smoking status was consistent with the objective measurement results in both genders. Among the various cut-off CO levels considered, 7 ppm was found to be the optimal level in both men and women. Conclusions. Our study showed that self-reporting is a reliable method for evaluating the smoking status of schizophrenia patients, regardless of gender. However, for precise assessment on the basis of CO levels in expired air, lower cut-off points may be better than the recommended ones. Key Words: Gender, schizophrenia, self-reporting, smoking, validity
Introduction It is reasonable to advise schizophrenia patients to quit smoking for health reasons, because patients who smoke regularly are at a higher risk of developing coronary heart diseases and stroke than the general population [1]. Further, ischemic heart disease is the most common cause of death among schizophrenia patients [2]. In clinical settings, psychiatrists usually determine the smoking status of patients through interviews or self-reported questionnaires filled out by the patients. Although Murray et al. reported that the self-reported smoking status is highly consistent with the smoking status determined by objective measurements in a non patient group [3], the self-reported smoking status is maybe more likely to be erroneous in schizophrenia patients because the patients’ responses largely
depend on their cognitive and/or mental condition [4]. However, to our knowledge, no study thus far has examined the accuracy of the self-reported smoking status of schizophrenia patients. In addition to the effects of schizophrenia, the basic and sensitive issue of gender-related differences should be considered when assessing the consistency between the self-reported smoking status and the true smoking status determined using biological markers [5,6]. The purpose of the present study is to compare the smoking status determined through self-reported questionnaires and objective measurements in schizophrenia patients, considering gender-related differences. In order to determine the validity of the self-reported smoking status, we monitored the carbon monoxide (CO) level in expired air.
Correspondence: Takeaki Takeuchi, MD, MPH, PhD, Department of Hygiene and Public Health, Teikyo University School of Medicine, 2-11-1 Kaga, Itabashi, Tokyo 173-8605, Japan. Tel: 81 3 3964 1211, ext. 2166. Fax: 81 3 3964 1058. E-mail: [email protected] (Received 24 July 2009 ; accepted 16 June 2010 ) ISSN 1365-1501 print/ISSN 1471-1788 online © 2010 Informa Healthcare DOI: 10.3109/13651501.2010.505342
Int J Psych Clin Pract Downloaded from informahealthcare.com by University of Connecticut on 10/28/14 For personal use only.
Self-reported smoking in schizophrenia
283
Materials and methods
Statistical analyses
Participants
First, the characteristics of the schizophrenia patients were descriptively analysed and compared between men and women. Second, to verify the relationship between self-reported smoking (smoking status as dichotomous values) and the CO level in expired air in our study, Spearman’s correlation analyses were performed in men and women, respectively. Then we compared those values to the values obtained from a previous study (correlation coefficient 0.71, P 0.01) [3] to assess the validity of the questionnaire. Third, to determine the optimal cut-off CO level in schizophrenia patients, the proportion of results in which the self-reported smoking status corresponded to the CO levels was analysed by using various cutoff levels. Further, to estimate the proportion of consistent results, we considered the self-reported smoking status as a fixed variable (assuming subjective report is trustable). We also calculated the proportion of “concordant patients”, that is, the number of self-reported smokers whose CO levels exceeded the cut-off level and self-reported non-smokers whose CO levels were below the cut-off level. The CO level that corresponded to the highest percentage of overlap was regarded as the optimal cut-off point [8]. Statistical analyses were conducted using STATA version 8.0 (StataCorp, College Station, TX), and P values of 0.05 in two-tailed tests were regarded as statistically significant.
We recruited 158 Japanese patients with schizophrenia (79 men and 79 women) from a psychiatric clinic located in a suburban area of Tokyo. The following patients were selected: (1) those who were treated by the physicians in charge between November 2007 and April 2008; (2) those who were diagnosed with schizophrenia as per the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision (DSM-IV-TR), during this period; (3) those with a stable medical condition (chlorpromazineequivalent dose, 1062.5 mg) and who had been on a constant drug regimen for more than 1 month; (4) those with no respiratory diseases that increase the CO levels, such as chronic obstructive pulmonary disease (COPD); and (5) those who agreed to participate in this study by signing the written informed consent form that described in detail the purpose and nature of the study and the risks associated with all the procedures. All the patients were hospitalized and isolated from environments that would increase the CO levels in expired air. None of the patients had regular jobs because their condition rendered them unable to lead normal social lives. Twenty-seven patients (17.1%) had a family history of schizophrenia, with the condition having affected third-degree relatives. This study was performed in accordance with the World Medical Association Declaration of Helsinki, and the protocol was approved by the Institutional Review Board of Teikyo University School of Medicine. Self-reported smoking status and CO measurement The patients were required to answer questions about their smoking status (classifying themselves as current smokers, former smokers, or non-smokers) and daily cigarette consumption, and the Fagerström test for nicotine dependence (FTND) was administered. CO levels in the expired air were measured with the Micro Smokerlyzer system (Bedfont Technical Instruments Ltd., Kent, UK); a psychiatrist proficient in using the equipment performed the measurements. The recommended cut-off level regarded as non smoking is less than 10 ppm [7]. The participants were instructed to inhale and hold their breath for 20 s and then exhale into the instrument. The endtidal CO reading in the expired air was measured during two trials, and the average of the two readings was used for the subsequent analyses. The average time intervals (meanSD) between the time they measured their CO levels and that of the last cigarette they smoked were 5.15.6 min in men and 4.0 8.2 min in women, respectively.
Results The patient characteristics are shown in Table I. In both men and women, 13 out of 79 people (16.5%) in both sexes smoked their first cigarette within 5 min of waking up. The number of self-reported current smokers was higher among the men than among the women (41 vs. 36%, P 0.05), and the mean daily cigarette consumption among smokers was also higher in the men than in the women (17.4 vs. 8.2, P 0.05). The age of the subjects, duration of disease, education level, FTND scores, and CO levels did not differ significantly between sexes. Correlation coefficients between smoking status and CO levels were both 0.76, p 0.01 in men and women, which were higher than that of the previous study [3]. Table II shows the percentage of results in which the self-reported smoking status was consistent with various CO cut-off levels. On the whole, the selfreported smoking status showed high consistency with the various cut-off levels of CO in the expired air. Of the various cut-off CO levels tested, 7 ppm was found to be the optimum level (with the lowest number of misclassifications) in both men and women. In men, the highest proportion of concordance
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Table I. Comparison of patient characteristics between men and women (N 158).
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Number (%), otherwise specified
Age: mean SD, years Duration of schizophrenia: mean SD, years 10 10–19 20–29 30 Educational level: mean SD, years Middle school High school Vocational school/2-year college University/higher Self-reported smoking data Smoking status Current Former smoker Non-smoker Daily consumption of cigarettes: mean SD FTND score: mean SD First cigarette after waking up, minutes 5 6–30 31–60 60 Difficulty of refraining from smoking, positive answer Hated to give up morning cigarettes, positive answer Daily cigarette consumption 10 11–20 21–30 31 Frequently smoking after waking up, positive answer Smoking in bed in spite of sickness, positive answer Carbon monoxide intake in terms of number of cigarettes: mean SD, ppm Smoking status Current Former smoker Non-smoker
Men (n 79)
Women (n 79)
P value
53.2 14.9 28.5 15.4 10 (12.6) 13 (16.5) 18 (22.8) 38 (48.1) 12.3 2.7 23 (29.1) 23 (29.1) 16 (20.3) 17 (21.5)
56.1 15.5 28.0 11.1 9 (11.4) 18 (22.8) 12 (15.2) 40 (50.6) 12.2 2.2 18 (22.8) 33 (41.8) 18 (22.8) 10 (12.6)
NS NS NS
32 (40.5) 22 (27.9) 25 (31.6) 17.4 28.9 2.2 3.1
28 (35.5) 5 (6.3) 46 (58.2) 8.2 11.9 1.9 2.8
0.05
13 13 1 52 13 20
(16.5) (16.5) (1.2) (65.8) (16.5) (25.3)
13 12 2 52 14 15
(16.5) (15.2) (2.5) (65.8) (17.7) (19.0)
NS NS
0.05 NS NS
NS NS
55 (69.6) 11 (13.9) 8 (10.1) 5 (6.3) 17 (21.5) 19 (24.1) 10.0 9.9
61 (77.2) 10 (12.7) 8 (10.1) 0 (0.0) 15 (19.0) 14 (17.7) 8.6 9.2
NS
NS NS NS
19.1 10.2 4.0 1.2 3.7 1.0
18.0 10.1 3.8 0.8 3.5 1.1
NS NS NS
FTND, Fagerström Test for Nicotine Dependence; SD, standard deviation. Two-tailed t-tests were used to compare the mean differences. For categorical variables, Fisher’s exact tests or proportion tests were used.
(96.2%) was found at CO levels of 7 and 8 ppm, followed by 9 ppm (94.9%). In women, the highest proportion of concordance (94.9%) was found at levels of 7 ppm, followed by 6, 8, 9, and 10 ppm (93.7%). After defining 7 ppm as the cut-off level of CO in expired air, comparison of the self-reported smoking status and CO levels revealed that seven people were misclassified. Among men, misclassification occurred only in the self-reported smokers with low CO levels (n 3, 3.8%). Further, among the three men who were misclassified, the mean daily cigarette consumption was 5.3 (range, 5–6 cigarettes per day) and the mean CO concentration was 5.3 ppm (range, 4–6 ppm). Among women, misclassification occurred in both the self-reported smokers with low CO levels (n 3, 3.8%) and the self-reported non-smokers with
high CO levels (n 1, 1.3%). Among the three female smokers with low CO levels, the mean daily cigarette consumption was 6.3 (range, 3–10 cigarettes per day) and the mean CO concentration was 5.3 ppm (range, 3–5 ppm). Among the female non-smokers with high CO levels, the daily consumption was 0 cigarettes and the CO concentration was 8 ppm. Discussion For decades, many studies have been conducted to determine how aware schizophrenia patients are of their smoking status. However, no study has focused on the validity of the self-reported smoking status in schizophrenia patients while taking into account gender-related differences. The results of the present
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Table II. Gender-wise comparison of the consistency in the smoking status assessed with a self-reported questionnaire and each CO cut-off level (N 158). Percentage consistently classified Men (n 79)
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Carbon monoxide cut-off levels 4 ppm 5 ppm 6 ppm 7 ppm 8 ppm 9 ppm 10 ppm 11 ppm 12 ppm 13 ppm
Women (n 79)
Reported smokers
Reported non-smokers
Total
Reported smokers
100.0 96.9 96.9 90.6 90.6 87.5 84.4 81.3 78.1 71.9
44.7 74.5 89.4 100.0 100.0 100.0 100.0 100.0 100.0 100.0
67.1 83.5 92.4 96.2 96.2 94.9 93.7 92.4 91.4 88.6
92.9 92.9 89.3 89.3 85.7 85.7 82.1 75.0 75.0 67.9
Reported non-smokers 56.9 86.3 96.1 98.0 98.0 98.0 100.0 100.0 100.0 100.0
Total 69.6 88.6 93.7 94.9 93.7 93.7 93.7 91.1 91.1 88.6
Note: To estimate the proportion of consistent results, we considered the self-reported smoking status as a fixed variable. We calculated the percentage of overlaps between self-reported smokers with high CO levels and self-reported non-smokers with low CO levels at specific cut-off points. The total was calculated as the total percentage of people who were accurately classified by both the self-reported questionnaires and CO measurements. Values greater than or equal to the listed cut-off values were considered indicative of smoking, as defined above.
study revealed that: (1) self-reporting is a reliable method for evaluating the smoking status of schizophrenia patients, regardless of gender; (2) for precise assessment of CO levels in expired air among schizophrenia patients, 7 ppm is a better cut-off level than the usual level of 10 ppm [8–10]; and (3) according to the responses in the self-reported questionnaires, male patients tended to smoke more cigarettes than female patients, but no gender-related differences were apparent in terms of the FTND or CO levels. Self-reporting by schizophrenia patients provided an accurate reflection of their smoking status, although some misclassifications occurred because of trade-off. The mean daily cigarette consumption was found to be relatively low among self-reported smokers with low CO levels (5.3 in men and 6.3 in women). One self-reported female non-smoker had a relatively low CO level of 8 ppm. Our second finding of lower cutoff CO levels being optimal seems interesting. It is widely accepted that hydrocarbons associated with cigarette smoking induce hepatic enzymes and therefore reduce the plasma concentrations of antipsychotics [11]. Although opposing theory that increased antipsychotics reduce hydrocarbons or cigarette smoking has not yet been proved, there could be the possibility. With regard to our third finding, previous studies have reported gender-related differences in the smoking habits of schizophrenia patients: the daily cigarette consumption is higher in men than in women [12]. However, we did not find any significant gender-related differences in the FTND scores and CO levels. Because of the small sample size of this study, our results may not provide a strong conclusion. But as a possible mechanism, CYP1A2 activity
may induce faster nicotine clearance in male smokers than in female smokers, thus buffering the increment in the FTND scores and CO levels [11,13]. Several limitations of this study should be taken into consideration. First, the sample size was relatively small, and all patients were selected from the same hospital. Our study, however, was conducted in a clinical setting, and the patients were diagnosed with schizophrenia as per the DSM-IV criteria; therefore, the diagnosis itself was accurate. Second, the patients did not maintain constant time intervals between cigarettes smoked. However, our CO measurements were conducted after the lunch period at the hospital, when most smokers smoke. Since CO measurements should be performed within 6–9 h of smoking in order to achieve an accurate assessment [14], all measurements in our study can be considered sufficiently accurate. Third, the wide SD of the daily consumption of cigarettes indicated that the distribution might have some outliers. However, our analyses excepting outliers (two outliers in men) did not change our results. Finally, the true smoking status should have been evaluated by measuring biochemical markers such as cotinine or thiocyanate. However, Murray et al. reported that the cotinine and CO levels are both reliable measures [3]. Moreover, all our study participants were inpatients at our hospital and were not exposed to any major CO source like vehicle exhaust or burning coal. Moreover, compared to the conventional biochemical markers like cotinine, it is more practical to measure the CO levels in expired air for evaluating the smoking status in clinical settings. In addition to those, CO analysis costs less than $1 per sample, while cotinine analysis costs $20 per sample [15]. Finally,
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we attempted to determine that a cut-off carbon monoxide value is based on the fact that self-reported responses are accurate. Although we tried to establish the robust condition of self-report accuracy, it was not sufficient enough. Thus, despite the abovementioned limitations, our study conclusively revealed that self-reporting is a useful method for evaluating the smoking status of schizophrenia patients. Further, when psychiatrists or medical professionals use CO levels in expired air for precise assessment of the smoking status, using lower cut-off points than the recommended ones may increase the accuracy of the data.
[2]
[3]
[4]
[5]
[6] [7]
Key points
• Self-reporting is a reliable method for evaluating •
•
the smoking status among schizophrenia patients, regardless of gender For precise assessment of CO levels in expired air among schizophrenia patients, 7 ppm seems to be a better cut-off level than the recommended level of 10 ppm According to the responses in the self-reported questionnaires, men tended to smoke more cigarettes than women, but no gender-related differences were observed in terms of the FTND scores or CO levels
Acknowledgement
[8]
[9]
[10]
[11]
None. [12]
Statement of interest None of the authors have any conflict of interests to declare.
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