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ORIGINAL ARTICLE
Year : 2013  |  Volume : 9  |  Issue : 1  |  Page : 84-89

A receiver operated curve-based evaluation of change in sensitivity and specificity of cotinine urinalysis for detecting active tobacco use


Department of Psychiatry, National Drug Dependence Treatment Centre, All India Institute of Medical Sciences, New Delhi, India

Date of Web Publication10-Apr-2013

Correspondence Address:
Yatan Pal Singh Balhara
Department of Psychiatry, National Drug Dependence Treatment Centre, All India Institute of Medical Sciences, New Delhi
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0973-1482.110384

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 > Abstract 

Background: Tobacco use has been associated with various carcinomas including lung, esophagus, larynx, mouth, throat, kidney, bladder, pancreas, stomach, and cervix. Biomarkers such as concentration of cotinine in the blood, urine, or saliva have been used as objective measures to distinguish nonusers and users of tobacco products. A change in the cut-off value of urinary cotinine to detect active tobacco use is associated with a change in sensitivity and sensitivity of detection.
Aim: The current study aimed at assessing the impact of using different cut-off thresholds of urinary cotinine on sensitivity and specificity of detection of smoking and smokeless tobacco product use among psychiatric patients.
Settings and Design: All the male subjects attending the psychiatry out-patient department of the tertiary care multispecialty teaching hospital constituted the sample frame for the current study in a cross-sectionally.
Materials and Methods: Quantitative urinary cotinine assay was done by using ELISA kits of Calbiotech. Inc., USA. We used the receiver operating characteristic (ROC) curve to assess the sensitivity and specificity of various cut-off values of urinary cotinine to identify active smokers and users of smokeless tobacco products.
Results: ROC analysis of urinary cotinine levels in detection of self-reported smoking provided the area under curve (AUC) of 0.434. Similarly, the ROC analysis of urinary cotinine levels in detection of self-reported smoking revealed AUC of 0.44. The highest sensitivity and specificity of 100% for smoking were detected at the urinary cut-off value greater than or equal to 2.47 ng/ml.
Conclusions: The choice of cut-off value of urinary cotinine used to distinguish nonusers form active users of tobacco products impacts the sensitivity as well as specificity of detection.

Keywords: Receiver operated curve, sensitivity, specificity, urinary cotinine


How to cite this article:
Balhara YS, Jain R. A receiver operated curve-based evaluation of change in sensitivity and specificity of cotinine urinalysis for detecting active tobacco use. J Can Res Ther 2013;9:84-9

How to cite this URL:
Balhara YS, Jain R. A receiver operated curve-based evaluation of change in sensitivity and specificity of cotinine urinalysis for detecting active tobacco use. J Can Res Ther [serial online] 2013 [cited 2019 Sep 20];9:84-9. Available from: http://www.cancerjournal.net/text.asp?2013/9/1/84/110384


 > Introduction Top


Tobacco use is the single largest preventable cause of mortality and morbidity globally. [1] Tobacco kills a third to half of those who use it. In the age group of 30-69 years, 1 in 5 males and 1 in 20 females die of tobacco related cause. [2] In terms of economic cost it is responsible for an annual global net loss of US$200 billion. [3] Tobacco use has been associated with various carcinomas including lung, esophagus, larynx, mouth, throat, kidney, bladder, pancreas, stomach, and cervix. In the Western nations, smoking is responsible for 90% of all cases of lung cancer. [4] The risk of dying from lung cancer is 22 times higher in male smokers and 12 times higher in female smokers compared with never smokers. [5] Lung cancer is the commonest cancer associated with tobacco use accounting for up to 20% of tobacco-related mortality. [1] Tobacco use, smoking as well as smokeless forms, is associated with increased risk of carcinoma in various Indian studies. [6],[7],[8],[9],[10],[11],[12]

Rates of tobacco use, specially smoking rates, are on the rise in low- and middle-income countries. [13] Of greater concern if the fact that by 2030 more than 80% of the world's tobacco-related deaths will be in low- and middle-income countries including India. [14] The prevalence of smokeless tobacco use in India is the highest in the world, with 26% of adults reporting being users of smokeless tobacco only. [7]

Tobacco control continues to be one of the major health challenges of modern times. The prevention of tobacco use in young people is the single greatest opportunity for preventing noncommunicable disease in the world today. [15]

Precise estimation of exposure to tobacco smoke is a concern for clinicians as well as epidemiologists. Concerns have been expressed about the reliability of self-report on use of tobacco products. [16] Such reports are likely to be inaccurate due to over- or underreporting, variability in the amount of smoke inhaled from a cigarette, duration for which tobacco product is kept in mouth among other factors. Assessment of passive exposure to tobacco smoke is considered even more problematic. [17]

Biomarkers such as concentration of cotinine in the blood, urine, or saliva have been used as objective measures to distinguish nonusers and users of tobacco products. [18],[19],[20] Most of the literature on tobacco is limited to cigarette smoking, and information on smokeless tobacco forms is limited.

Urinary cotinine level is a widely used biomarker. A good correlation exists between urinary cotinine and daily tobacco consumption. [20] However, use of this biomarker among psychiatric patients is limited. [21] Screening of active tobacco use among psychiatric patients is important as it is the most prevalent substance abuse disorder among individuals with mental illness. [22] Epidemiological studies have found smoking rates among psychiatric patients to be twice that of the general population. [23]

The existing literature recommends a wide range of cut-off values for urinary cotinine to distinguish nonusers from active users of tobacco products. The reported values range from 20-550 ng/ml. [20],[24],[25],[26],[27],[28],[29],[30],[31],[32],[33],[34],[35] A change in the cut-off value is associated with a change in sensitivity and sensitivity of detection. It has been recommended that the validation cut-off value of urinary cotinine should be estimated separately for racially different groups. [36] The available cut-off values are based on studies from western countries. Hence it is imperative to specify the appropriate cut-off values for the Indian population.

The current study aimed at assessing the impact of using different cut-off thresholds of urinary cotinine on sensitivity and specificity of detection of smoking and smokeless tobacco product.


 > Materials and Methods Top


All the male subjects attending the psychiatry out-patient department of the tertiary care multispecialty teaching hospital constituted the sample frame for the current study. All male patients aged 18 or more, coming for the follow-up visit were approached for participation in the study. Those willing to participate and giving informed consent were included in the study. Finally 124 urine samples were included in the study.

The study subjects were asked about their recent tobacco use during the past week. Active tobacco use was defined as daily use of tobacco products. Information was gathered for both smoking and smokeless forms of tobacco. Those reporting recent tobacco use were asked "How many cigarettes/biri/guthka/etc do you use per day?"; "Which is your most preferred tobacco product?" Additionally they were assessed for severity of dependence using the Fagerstrom test for nicotine dependence (FTND) (smoking as well as smokeless). FTND-smoking is a widely used six-item questionnaire used to screen for severity of dependence on smoked tobacco. [37] FTND-smokeless (FTND-ST) is a nine-item instrument used to evaluate the level of nicotine dependence for smokeless tobacco. [38]

A total of 50 ml of urine sample was collected from each subject under supervision and were submitted for laboratory analysis. Quantitative urinary cotinine assay was done by using ELISA kits of Calbiotech Inc., USA which uses solid phase competitive ELISA. Assay was carried out as directed by the manufacturers. The minimum detection limit of cotinine in the assay was 2 ng/ml. The immunological methods have been found to have minimal cross-reactivity with nicotine and other metabolites. Also this technique is sensitive enough to detect environmental tobacco smoke (ETS) exposure. [39]

Data were analyzed using SPSS ver 17. We used the receiver operating characteristic (ROC) curve to assess the sensitivity and specificity of various cut-off values of urinary cotinine to identify active smokers and users of smokeless tobacco products. The analysis was carried out separately for smoking and smokeless forms of tobacco. The level of statistical significance was kept at P < 0.05.

Conditions of anonymity and confidentiality as specified in the institutional guidelines were ensured during the study.


 > Results Top


Urine samples of 124 male subjects attending the psychiatry out-patient department were included in analysis. The mean age of study subjects was 31.24 (SD ± 11.91) years. Eighty (64.5%) of the subjects were from urban background and eighty one (65.3%) were married. Self-reported recent smoking was reported by 22 (17.7%) of the subjects. Self-reported use of smokeless tobacco products was reported by 20 (16.1%) of the subjects. The mean FTND scores were 2.69 (SD 1. ± 35) and 3.29 (SD ± 1.86) for smoking and smokeless forms.

ROC analysis of urinary cotinine levels in detection of self-reported smoking provided the area under curve (AUC) of 0.434 [Figure 1]. Similarly, the ROC analysis of urinary cotinine levels in detection of self-reported smoking revealed AUC of 0.44. Both these values are lower than the true specified area of 0.50 [Figure 2] and [Table 1].
Figure 1: Receiver operated curve (ROC) for detection of smoking using cotinine urinalysis

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Figure 2: Receiver operated curve (ROC) for detection of smokeless tobacco products using cotinine urinalysis

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Table 1: Area under the curve (AUC) statistics for smoking and smokeless tobacco

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Analysis of the coordinates of ROC revealed a variation in sensitivity as well specificity of the cut-off value of urinary cotinine used to detect the presence of smoking and use of smokeless tobacco products by the study subjects [Table 2].
Table 2: Coordinates of the receiver operated curve (ROC) for various cut-off values of urinary cotinine for smoking and smokeless tobacco product

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The highest sensitivity and specificity of 100% for smoking were detected at a urinary cut-off value greater than or equal to 2.47 ng/ml. Both sensitivity and specificity declined with an increase in the cut-off threshold. The sensitivity and specificity of 90% were seen at the cut-off value greater than or equal to 12.54 ng/ml. Other sensitivity and specificity values included 68% and 84% (for 20.91 ng/ml); 50% and 58% (for 50.59 ng/ml); 45% and 54% (for 94.34 ng/ml); 45% and 53% (for 105.56 ng/ml); 36% and 48% (for 220.10 ng/ml); 36% and 43% (for 360.80 ng/ml); and 36% and 40% (for 710.44 ng/ml).

The highest sensitivity and specificity of 100% for the smokeless tobacco products were detected at a urinary cut-off value greater than or equal to 2.47 ng/ml. A sensitivity and specificity of 90% were seen at the cut-off value greater than or equal to 12.54 ng/ml. Other sensitivity and specificity values included 75% and 84% (for 20.91 ng/ml); 60% and 56% (for 50.59 ng/ml); 55% and 52% (for 94.34 ng/ml); 55% and 51% (for 105.56 ng/ml); 40% and 47% (for 220.10 ng/ml); 30% and 44% (for 360.80 ng/ml); and 25% and 42% (for 710.44 ng/ml).


 > Discussion Top


The current study aimed at assessment of the impact of the cut-off value of urinary cotinine on sensitivity and specificity to detect active smoking and use of smokeless tobacco products.

Tobacco use is a major contributor to multiple carcinomas including lung, esophagus, larynx, mouth, throat, kidney, bladder, pancreas, stomach, and cervix. The probability of developing tobacco-related cancers among 35-70 years old has been found to be 4.75% and 2.16% in males and females respectively in India. [9] An Indian study reported that among a cohort of patients with nasopharyngeal carcinoma majority of patients (47.0%) chewed tobacco in different forms and (51.0%) smoked at least for 15 years. [11] Another retrospective study on risk habits among oral cancer patients in Karnataka found that prevalence of oral cancer was higher among elderly males predominantly with risk habits of betel quid/tobacco chewing and smoking for more than 10 years. [6] Smoking as well as smokeless tobacco use has been associated with gastric carcinoma in an Indian study. [10] Hookah smokers were found to be have 4.2 times risk of lung cancer compared to nonsmokers in a study from Kashmir Valley. [8]

Smoking cessation has been associated with up to 32% reduction in all-cause mortality at 5 years of follow-up. [40] Smoking cessation helps reduce the risk of canrcinomas. The risk of lung cancer declines steadily following smoking cessation such that after about 10 years of abstinence, the risk of lung cancer is between 30% and 50% of that for continued smokers. [41] It has been seen that smoking cessation reduced total mortality by 66% and the risk of recurrence or a second lung primary by 46% compared with continued smokers in patients who are diagnosed with early stage nonsmall cell lung cancer. [42] A study from Mumbai reported oral precancers among 40% of tobacco users. After 1 year of workplace tobacco cessation intervention, 80% of oral precancers had regressed. [12]

Socially undesirable behaviors such as tobacco use are prone to underreporting. [43],[44] Trends of underestimation have been reported when smoking prevalence is based on self-report alone. [16],[45] Use of biomarkers has been recommended to screen individuals for active tobacco use. [46] Urinary cotinine has been a widely used biomarker for this purpose.

The existing literature has recommended a wide range of cut-off thresholds of urinary cotinine to assess exposure to tobacco products. The recommended cut-off values have ranged from a low of 20 ng/ml to a high of 550 ng/ml. [14],[18],[20],[24-35]

The sensitivity as well as specificity, as assessed by the co-ordinates of the ROC, for both smoking and smokeless tobacco forms was found to reduce with an increase in the cut-off threshold value of urinary cotinine in the current study. The maximum sensitivity and specificity of 100% were seen at urinary cotinine values greater than or equal to 2.47 ng/ml. However use of such a low urinary cotinine value would not be appropriate to detect the direct smoking or use of smokeless tobacco products. Exposure to environmental tobacco smoke (ETS) is likely to result in these values. This would lead to a high false-positive rate of detection. The proposed threshold values to distinguish between nonsmokers exposed or not exposed to ETS range from 5 ng/ml [47] to 10 ng/ml. [48],[49]

The lowest cut-off threshold of urinary cotinine recommended to distinguish smokers from nonsmokers and passive smokers has been 20 ng/ml. [33] Other studies have recommended a cut-off value of 30 ng/ml, [30] 50 ng/ml, [28] and 90 ng/ml. [27] However, the most commonly recommend range of cut-off values is 100-500 ng/ml. [31],[32],[33],[34] Savitz [34] has recommended a range of 50-500 ng/ml for this purpose. Other values cited in the literature include 248 ng/ml [29] and 350 ng/ml. [24] The highest cut-off value of urinary cotinine to distinguish smokers from nonsmokers is 550 ng/ml. [35]

In the current study a sensitivity and specificity of 90% were detected at the cut-off value of 12.54 ng/ml for both smoking and smokeless tobacco. This value is lower than the lowest recommended cut-off value of 20 ng/ml in the literature. [33] At the cut-off threshold of 20 ng/ml, we obtained the sensitivity of 68% and specificity of 84% for smoking. At the same cut-off value the sensitivity and specificity were 75% and 82%, respectively for smokeless tobacco.

We could not assess the sensitivity and specificity for the exact co-ordinates of 100 ng/ml, 200 ng/ml, 550 ng/ml, and 550 ng/ml. This was so because none of the samples on the study delivered these values on cotinine level assessment. Instead we used the nearest possible co-ordinate for these values. The sensitivity and specificity values at all these cut-off values were low for both smoking and smokeless tobacco forms.

Several studies show that urinary cotinine levels in nonsmokers are always less than 100 ng/ml urine. This is true despite rather high levels of passive exposure in some cases. [50],[51] In the current study the sensitivity and specificity at 105.56 ng/ml were 45% and 53%, respectively for smoking. The values were 55% and 51% for smokeless tobacco forms.

Interestingly the AUC for the ROC of urinary cotinine levels was low for both smokeless and smokeless forms of tobacco. Concerns have been expressed about reliability of the self-report of use of tobacco products. [16],[21] The low AUC observed in the current study are reflection of the same observation. This issue further raises some concerns. What should be the ideal cut-off threshold of urinary cotinine to identify active users of tobacco products among patients suffering from psychiatric disorder? The recommended cut-off values in the literature are based on subjects not having diagnosed psychiatric disorders. Could the same cut-off values be applied for the psychiatric patients as well?

It has been recommended that physicians should screen all patients for tobacco use and offer appropriate tobacco cessation services. [23] However, missed opportunities of offering tobacco cessation support have widely been cited in the published literature. [52]

Selection of the cut-off value of urinary cotinine for screening of active tobacco use has important clinical implications. While setting a threshold too high would lead to missing a large proportion of active users, am erroneously low threshold would yield a high false positive value. The tobacco cessation services are limited in the India. [53] There is a need to have appropriate screening measures in order to ensure judicious use of these resources.

There is a need to formulate appropriate cut-off values of urinary cotinine for smokers as well as smokeless tobacco product users. Carefully documented daily use of tobacco products could help develop correlation between the amount of tobacco consumed and urinary cotinine level. These studies should also take into consideration exposure to environmental smoke including the SHS.

A recent study has recommended different threshold values of urinary cotinine to distinguish nonsmokers, passive smokers, and active smokers. The values which enabled differentiation of these groups were 50 ng/ml to differentiate nonsmokers from passive smokers; 170 ng/ml to divide the group of passive smokers into two subgroups, i.e., minimally and highly exposed to environmental tobacco smoke; 550 ng/ml to differentiate passive smokers from active smokers and 2100 ng/ml to divide the group of active smokers into two subgroups, i.e., minimally and highly exposed to tobacco smoke. Similarly age appropriate cut-off scores for biomarkers for distinguishing active users of tobacco products have also been recommended. [54]

The current study had certain strength. We recruited consecutive sample for the study purpose. Both smoking and smokeless tobacco forms were assessed. The study was carried out among psychiatric patients. There is limited literature on smokeless tobacco forms and psychiatric patients.

However, the study did not include female patients due to logistic issues. Also exposure to environmental smoke could not be quantified. The findings are from a single site and hence need to be replicated before they could be generalized to other settings.

The future studies should include both male and female subjects. Quantitative information on exposure to environmental smoke would also provide additional understanding into the issue.


 > Conclusion Top


The choice of cut-off value of urinary cotinine used to distinguish nonusers form active users of tobacco products impacts the sensitivity as well as specificity of detection. In order to arrive at cut-off values appropriate for psychiatric patients in Indian settings, the cut-off values cited in existing literature need to be relooked.

 
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    Figures

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    Tables

  [Table 1], [Table 2]


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