Abstract
BACKGROUND:
Nicotine concentration in hair is a useful marker of tobacco exposure. Detection of nicotine in the hair of non-smokers indicates passive smoking. Accurate measurement of nicotine among active and passive smokers can help in smoking cessation programs or programs designed to prevent secondhand smoke exposure.
OBJECTIVE:
To establish, using high-performance liquid chromatography-ultraviolet detection (HPLC/UV), a hair nicotine cut-off value to distinguish active from passive smokers.
METHODS:
Hair samples were collected from randomly chosen Japanese men (
RESULTS:
There were 69 active smokers and 123 passive smokers. The nicotine and cotinine concentrations in hair were significantly higher in active than in passive smokers (
CONCLUSION:
Nicotine and cotinine concentrations in hair clearly distinguished active from passive smokers.
Introduction
Smoking is a serious public health issue that is widely recognized as a preventable risk factor for serious illnesses, such as cancer [1, 2] and cardiovascular disease [3, 4]. Exposure to passive smoke is also known to lead to numerous health problems, particularly among children [5, 6]. Distinguishing active smoking from passive smoking in the general population via screening tests has a number of benefits, including establishing the effectiveness of smoking cessation interventions. In addition, early screening may prevent exposure to further passive smoking for non-smokers. However, in order to distinguish active from passive smokers in the general population, it is important to biologically monitor smoking exposure.
Although previous studies have reported that nicotine and cotinine levels can be measured in the blood, urine, and saliva of smokers [7, 8, 9], the amount of nicotine and cotinine in these samples may reflect acute exposure to smoking rather than habitual smoking. Furthermore, because levels of nicotine in hair remain stable over a long period, it has been suggested that hair testing may be useful for the biological monitoring of nicotine exposure in the medium and long term [10, 11, 12, 13].
The measurement of nicotine and cotinine concentrations in hair samples is usually conducted using gas chromatography with mass spectrophotometry (GC/MS) or high-performance liquid chromatography with mass spectrophotometry (HPLC/MS). However, because of their expense, these methods are performed only in special laboratories [14, 15, 16]. In light of this, we previously established a method of high-performance liquid chromatography with ultra violet detection (HPLC/UV) with column-switching to measure nicotine and cotinine in hair [12]. Our results showed that this method was advantageous in its simplicity and low cost whilst maintaining a sensitivity similar to that of GC/MS and HPLC/MS. We also detected an average of 1.60 ng/mg of nicotine in hair samples of non-smokers and therefore concluded this method was a useful tool to measure the effect of secondhand smoke on non-smokers. However, the cut-off value for distinguishing active from passive smokers is yet to be determined – such classification would be beneficial in assessing the smoking status of those in smoking cessation programs.
Therefore, this study aimed to assess smoking status by measuring nicotine and cotinine in the hair of Japanese men selected from the general population, using HPLC/UV with column-switching. We also aimed to determine the nicotine cut-off value to distinguish active from passive smokers using a receiver operating characteristics (ROC) analysis, as this test could be used as a screening tool.
Materials and methods
Subjects
A total of 2,000 Japanese men were chosen from government Basic Resident Registries using cluster random sampling; the sample size calculation was based on the findings of a previous pilot study. During the period 2009–2011, a questionnaire about smoking status was administered to patients at their homes, and hair samples were taken from subjects during home visits. Questionnaires were anonymous to protect private information, and informed consent was obtained from each subject. The study was approved by the appropriate ethics committee. Completed questionnaires were collected from 1,355 participants (response rate 68%), and hair samples were collected from 210 participants (collection rate, 15.5%). Eighteen samples were not used in the analysis because of gray hair, dyed hair, or an insufficient quantity of hair, leaving 192 samples for analysis. Active smokers were identified as subjects who answered “Yes” or “Sometimes” to the question “Do you smoke tobacco presently?”. Those who answered “No” to this question or the question "Have you ever smoked tobacco?" were identified as passive smokers.
Questionnaire
The questionnaire included items on age, height, weight, education, occupation, and annual income. Items relating to health, including past history of cardiovascular disease, knowledge of smoking-related risks, and alcohol consumption history, were also collected. A history of cardiovascular disease was defined as having been diagnosed with hypertension, angina, or another heart disease in the past year. Knowledge of smoking-related risks was assessed by the question “Do you think that smoking causes serious disease?” with response options of “Yes”, “No”, or “Unknown”. Alcohol consumption was categorized into six groups: everyday, several times a week, several times a month, several times a year, no drinking for more than a year, and never had a drink. Because of the relationship between smoking and obesity [17], we also calculated body mass index (BMI) from height and weight (kg/m
Hair sampling
We previously developed a hair-cutting kit to collect hair samples by affixing hair to the back of the head with tape (15 cm

Stages of hair preparation for testing.
Characteristics of active and passive smokers
Characteristics of active and passive smokers
Summary measures are given as mean
Figure 1 shows the stages involved in the hair preparation for testing. Hair samples were placed in test tubes and washed three times using 3 mL of dichloromethane (133-02441, Wako Pure Chemical Industries, Ltd., Osaka, Japan). Hair samples (25
Samples were analyzed for nicotine and cotinine using HPLC/UV with the column-switching method [12]. We used the HPLC LC-2000 Plus Series, the UV-2075 detector (set at 260 nm), and the HV-2080-01 column selection unit (all from JASCO, Tokyo, Japan). The concentrating column was introduced using the Develosil ODS-UG-5 Column (1 cm
Statistical analysis
Differences in the mean concentrations of nicotine, cotinine, and nicotine plus cotinine as well as age, BMI, and education among active and passive smokers were assessed using

ROC curve for nicotine and nicotine plus cotinine in hair as predictors of smoking. Nicotine: AUC
Characteristics of active and passive smokers among the general population of Japanese men
Among the 192 subjects, there were 69 (36%) active smokers and 123 (64%) passive smokers. The characteristics of the participants are shown in Table 1. The mean
The concentrations of nicotine, cotinine, and the sum of nicotine plus cotinine were significantly higher among active smokers than among passive smokers. The means
Nicotine and nicotine plus cotinine in hair as predictors of smoking
The AUCs for nicotine and the sum of nicotine plus cotinine were 0.92 (95% CI, 0.88–0.96) and 0.93 (95% CI, 0.89–0.97), respectively (Fig. 2). The cut-off values for nicotine and the sum of nicotine plus cotinine were 5.68 ng/mg (sensitivity, 94.2%; specificity, 87.0%) and 6.39 ng/mg (sensitivity, 92.8%; specificity, 87.0%), respectively. In addition, these cut-off values were found to be optimal for distinguishing active from passive smokers.
Discussion
Our results show that nicotine and cotinine are clearly detected in the hair of Japanese men who actively smoke. This is consistent with previous studies showing that nicotine from smoking accumulates in the hair [20]. We found that active smokers were less likely than passive smokers to report knowledge of smoking-related risks. This is in contrast to earlier work in Japan where more smokers than non-smokers understood the hazards of smoking [21, 22]. Our results may be indicative of an increased awareness of smoking risks from recent public health campaigns in Japan, or it may be that smokers deny the harmful effects of smoking and are under-reporting their true knowledge of smoking risks.
This study identified the appropriate cut-off value for separating active from passive smokers among adult Japanese men. Such a cut-off value may be useful for establishing adherence to early smoking cessation interventions, and, hence, may improve the effectiveness of such interventions. Our findings also support the notion that nicotine in hair can effectively be used to screen for long-term exposure to smoking via a simple and inexpensive test.
Previous studies have demonstrated that cut-off values vary substantially with different biological samples and may reflect acute exposure to smoking. For example, cut-off values of cotinine to distinguish active from passive smokers range from 13.7 ng/mL in blood [23, 24, 25] to 10.0 ng/ML in plasma [23] and to 3.08 ng/mL in serum [24] samples. Optimal cut-off values for cotinine in urine and saliva also vary widely between different populations [23, 26, 27, 28, 29]. Measurement of exhaled carbon monoxide is a useful technique for monitoring smoking; it can determine whether an individual has smoked in the previous 8 hours [30, 31]. However, it is not suitable as a tool for long-term smoking evaluation because measurement of carbon monoxide cannot evaluate smokers who have not smoked in the preceding 8 hours. Thus, our findings demonstrate that hair is more useful than other biological samples for measuring exposure to tobacco xenobiotics.
Furthermore, although the liver metabolizes 80–90% of nicotine to cotinine [32], there is a great deal of individual variation. Measurement of nicotine in blood, urine, and saliva samples is prone to inaccuracy due to the short half-life of nicotine; therefore, measuring cotinine is more reliable as it has a longer half-life (averaging 16–19 hours) [33, 34, 35]. Moreover, only approximately 10% of nicotine is excreted in the urine [32]. However, our results indicate that nicotine is stable in hair. This is most likely because nicotine has a high affinity for melanin in hair. In addition, the amount of nicotine in hair accurately reflects the amount of nicotine absorbed from the lungs [36]. Thus, the total concentration of nicotine and cotinine in hair can be used to determine smoking status. However, it seems that only nicotine is useful as an index for smokers because cotinine loses its affinity for melanin and seldom accumulates in hair. In addition, findings from the ROC analysis show that the sensitivity and specificity of nicotine plus cotinine for distinguishing active from passive smokers was similar to that of nicotine alone, suggesting that nicotine in hair can serve as an index variable. Furthermore, some reports show that nicotine concentration in hair stabilizes over the long term, thus reflecting smoking exposure concentration [10, 37, 38, 39, 40].
To the best of our knowledge, no previous study has examined the cut-off value of nicotine and/or cotinine in hair using an ROC analysis. The AUC and the cut-off value of nicotine in hair were shown to be 0.92 ng/mg and 5.68 ng/mg, respectively. The ROC curve for nicotine in hair was convex at the upper left, corresponding to a sensitivity of 94.2% and specificity of 87.0%. Thus, nicotine concentration in hair may be more suitable for distinguishing active from passive smokers compared with total nicotine plus cotinine concentration in hair.
Research on smoking status among patients who visit health care facilities may be prone to selection bias [41]; however, our subjects were community-dwelling residents. The results of the present study indicate that nicotine levels in hair may be a practical way to determine smoking status in the general population. The results of a previous study indicated that taking action against smoking at the local level is important [42]. Our methods and cut-off value could be used to screen for long-term exposure among smokers at the local level. Our results also show that it is possible to intervene early to encourage smoking cessation and to prevent additional effects related to passive smoking if active and passive smokers are clearly distinguished in the general population. The classification of active and passive smoking can be carried out directly through hair samples, thus avoiding any misclassification of smoking habits as a source of potential bias.
This study has a number of limitations that need to be considered. First, our sample was restricted to men and therefore we cannot generalize these findings to women. Previous research has shown a sex difference in the susceptibility of developing lung disease following exposure to nicotine [43, 44]. In addition, women have been shown to metabolize the chemical substances contained in cigarettes differently to men [45]. Second, as the gene CYP2A6 polymorphism, that helps to metabolize nicotine to cotinine, reportedly differs between Japanese and non-Japanese individuals [46, 47, 48], the cut-off value may differ in different populations.
In conclusion, we were able to distinguish active smokers from passive smokers in the general population by measuring the hair concentration of nicotine using the HPLC/UV with column-switching method. Our results suggest that nicotine in hair is a more valuable index for smoking evaluation than other biological measures. The optimal cut-off value had both high sensitivity and specificity, suggesting that nicotine in hair can be used as an effective and noninvasive screening tool to assess current smoking status and monitor adherence to smoking cessation programs.
