Validity of Self-reported Smoking Status among Participants in a Lung Cancer Screening Trial

Abstract

Lung cancer remains a devastating disease associated with substantial morbidity and mortality. Recent research has suggested that lung cancer screening with spiral computed tomography scans might reduce lung cancer mortality. Studies of lung cancer screening have also suggested that significant numbers of participants quit smoking after screening. However, most have relied solely on self-reported smoking behavior, which may be less accurate among participants in lung cancer screening. To assess the validity of self-reported smoking status among participants in a lung cancer screening trial, this study compared self-reported smoking status against urinary cotinine levels. The sample included 55 consecutive participants enrolled in a randomized clinical trial comparing annual spiral computed tomography and chest X-ray for lung cancer screening. Participants were a mean of 59 years of age and predominantly Caucasian (96%) and male (55%). Self-reported smoking status was assessed before and after participants learned of the purpose of the biochemical verification study. Using urinary cotinine as the "gold standard," the sensitivity and specificity of self-reported smoking status were 91% and 95%, respectively (kappa = 0.85, P < 0.001, 95% confidence interval = 0.71-0.99). Total misclassification rate was 7%. However, three of the four misclassified participants reported concurrent use of nicotine replacement strategies. Eliminating these cases from the analysis revealed sensitivity of 100% and specificity of 95% (kappa = 0.96, P < 0.001, 95% confidence interval = 0.88-1.00). In conclusion, self-reported smoking status among participants in a lung cancer screening trial was highly consistent with urinary cotinine test results.

Full text

Validity of Self-reported Smoking Status among
Participants in a Lung Cancer Screening Trial
Jamie L. Studts,1
,
2Sameer R. Ghate,2Jaime L. Gill,2Christina R. Studts,2
,
3
,
4
Christopher N. Barnes,2
,
3A. Scott LaJoie,2
,
5Michael A. Andrykowski,6
and Renato V. LaRocca7
1Division of Hematology/Oncology, Department of Medicine, University of Louisville School of Medicine; 2Behavioral
Oncology Program, James Graham Brown Cancer Center; 3Department of Bioinformatics and Biostatistics, University
of Louisville School of Public Health and Information Sciences; 4Kent School of Social Work, University of Louisville;
5Department of Health Promotion and Behavioral Sciences, University of Louisville School of Public Health and
Information Sciences; 6Department of Behavioral Science, University of Kentucky College of Medicine; and
7Kentuckiana Cancer Institute, PLLC, Louisville, Kentucky
Abstract
Lung cancer remains a devastating disease associated with
substantial morbidity and mortality. Recent research has
suggested that lung cancer screening with spiral computed
tomography scans might reduce lung cancer mortality.
Studies of lung cancer screening have also suggested that
significant numbers of participants quit smoking after
screening. However, most have relied solely on self-
reported smoking behavior, which may be less accurate
among participants in lung cancer screening. To assess the
validity of self-reported smoking status among participants
in a lung cancer screening trial, this study compared self-
reported smoking status against urinary cotinine levels. The
sample included 55 consecutive participants enrolled in a
randomized clinical trial comparing annual spiral computed
tomography and chest X-ray for lung cancer screening.
Participants were a mean of 59 years of age and predom-
inantly Caucasian (96%) and male (55%). Self-reported
smoking status was assessed before and after participants
learned of the purpose of the biochemical verification
study. Using urinary cotinine as the ‘‘gold standard,’’ the
sensitivity and specificity of self-reported smoking status
were 91% and 95%, respectively (k= 0.85, P< 0.001,
95% confidence interval = 0.71-0.99). Total misclassification
rate was 7%. However, three of the four misclassified
participants reported concurrent use of nicotine replace-
ment strategies. Eliminating these cases from the analysis
revealed sensitivity of 100% and specificity of 95% (k=0.96,
P< 0.001, 95% confidence interval = 0.88-1.00). In conclu-
sion, self-reported smoking status among participants in
a lung cancer screening trial was highly consistent with
urinary cotinine test results. (Cancer Epidemiol Biomarkers
Prev 2006;15(10):1825–8)
Validity of Self-reported Smoking Status among
Participants in a Lung Cancer Screening Trial
Lung cancer is a devastating illness associated with substantial
morbidity and mortality. In 2006, f174,470 Americans will be
diagnosed with lung cancer, and another 162,460 will die from
the disease (1). Improved survival with early diagnosis has
prompted exploration of lung cancer screening technologies
(2-5). In addition to the medical implications of early detection,
participation in screening programs may be associated with
decreased smoking rates (6-9), although some have suggested
that negative screening results may actually lead to continu-
ation of or return to smoking (6).
Most studies exploring changes in smoking status associated
with screening have relied solely on participant self-report of
smoking status. The veracity of self-reports is often questionable
in situations involving social pressure or medical disapproval
(10-13). In these high-demand situations, studies have consis-
tently suggested that smoking behavior is underreported
(12-18). Although inaccurate self-reported smoking status in
the general population occurs relatively infrequently (15, 19),
the lung cancer screening context may constitute a high-demand
situation, a condition under which biochemical verification is
recommended (16). Thus, the veracity of self-report among
participants in screening programs should be explored to
determine accurately any effects of participation in lung cancer
screening on smoking behavior. This question is especially
important given the expanding opportunities for lung cancer
screening and the ongoing National Lung Screening Trial.
Only one study exploring the effects on smoking behavior of
participation in lung cancer screening has employed biochem-
ical verification of smoking status (9) using testing of carbon
monoxide levels. Although findings suggested that self-reported
smoking status among participants in lung cancer screening
was valid, carbon monoxide testing is not recommended in
some contexts due to limited sensitivity and specificity, as well
as inability to detect use of smokeless tobacco products (16).
More specific and sensitive measures of tobacco use involve
testing for cotinine, a metabolite of nicotine that can be
measured in plasma, saliva, or urine (16). Cotinine has a half-
life of f20 hours, allowing detection in smokers for up to a week
from the last smoking episode (20). Studies comparing non-
smokers and smokers have consistently reported that cotinine in
the urine, saliva, or plasma can distinguish active smokers from
nonsmokers (13, 14, 20-24). In addition, cotinine has been shown
to be more sensitive and specific than carbon monoxide
monitoring for measuring smoking status (10, 16). One
inexpensive, reliable, and valid measurement tool for cotinine
is the urinary cotinine test strip. Test strips have been shown to
compare favorably to gas chromatography/mass spectrometry
testing for cotinine (18, 25), with sensitivity and specificity of
urinary cotinine test strips ranging from 90% to 97% in
identifying smokers when used with a 100 ng/mL threshold.
1825
Cancer Epidemiol Biomarkers Prev 2006;15(10). October 2006
Received 5/17/06; revised 7/27/06; accepted 8/8/06.
Grant support: Kentucky Lung Cancer Research Board.
The costs of publication of this article were defrayed in part by the payment of page charges.
This article must therefore be hereby marked advertisement in accordance with 18 U.S.C.
Section 1734 solely to indicate this fact.
Note: These data have been previously presented at the 2006 American Society of Preventive
Oncology meeting in Bethesda, Maryland.
Requests for reprints: Jamie L. Studts, Behavioral Oncology Program, James Graham Brown
Cancer Center, Room 422, 529 South Jackson Street, Louisville, KY 40202. Phone: 502-852-8094;
Fax: 502-562-4368. E-mail: jamie.studts@louisville.edu
Copyright D2006 American Association for Cancer Research.
doi:10.1158/1055-9965.EPI-06-0393
on May 15, 2017. © 2006 American Association for Cancer Research. cebp.aacrjournals.org Downloaded from

Research Question
The accuracy of self-reported smoking behavior among
participants in lung cancer screening has not been thoroughly
explored. This study compared self-report and biochemical
verification using urinary cotinine levels measured with the
NicAlert strip (Nymox, Maywood, NJ). The research question
addressed whether self-reported smoking status among a
sample of participants in a randomized clinical trial of lung
cancer screening would be concordant with biochemical
measurement of smoking status.
Materials and Methods
Procedure
Parent Study: Jewish Hospital Lung Cancer Screening and Early
Detection Study. The current report describes a substudy of the
Jewish Hospital Lung Cancer Screening and Early Detection
Study (JH-LCSS; 26), a randomized prospective trial of lung
cancer screening comparing annual chest X-ray to annual spiral
computed tomography scanning in patients at high-risk of
developing lung cancer. The JH-LCSS is unique in its focus on a
sample of individuals at very high-risk of lung cancer, as
defined by a minimum 30-pack-year smoking history and
impaired respiratory function (FEV
1
/FVC ratio of <70% or
FEV
1
<80% of predicted normal values). Participants in the JH-
LCSS were recruited using community and regional advertis-
ing efforts, including television, newspaper, radio, and direct
mailings. Following a negative or stable baseline chest X-ray,
participants were randomly assigned to receive annual chest X-
ray or spiral computed tomography for a period of 3 to 5 years.
Biochemical Validation of Self-reported Smoking. Participants
due for annual screening in September 2004 were eligible for
this substudy, which was approved by a human studies
committee at the University of Louisville. In late August, all
104 eligible participants were informed by mail of the
opportunity to participate in a substudy. The purpose of the
substudy was not disclosed in the letter. A research assistant
met 55 of the 58 participants who attended their scheduled
screening appointments in September; three participants
attended appointments but were missed by the research
assistant, and the remaining 46 potential participants did not
attend their screening appointments. Each of the 55 partic-
ipants provided informed consent, completed a substudy
questionnaire, and provided a urine sample. Gift certificates
valued at US$20 were provided to substudy participants.
Measures. Data from two questionnaires were used in these
analyses. Within the 30 days preceding the substudy,
participants had completed the parent study questionnaire
(Annual Survey of Smoking Behavior or ASSB), given annually
by mail in the month before screening. On the day of
screening, participants completed the substudy questionnaire
(Substudy Smoking Behavior Questionnaire or SSSBQ). The
use of two questionnaires allowed the important comparison
of self-reported smoking status before and after participants
were informed of the biochemical validation component of the
substudy.
ASSB. Asingleitemfromtheparentstudyannual
questionnaire was used: self-reported smoking status. Partic-
ipants selected their current smoking status from three
options: current smoker, quit <6 months ago, or quit >6
months ago. This item was used to compare self-reported
smoking status before and after being informed of the purpose
of the substudy.
SSSBQ. Each participant completed a questionnaire regard-
ing smoking and smoking-related behaviors before biological
sample collection. The principal item measuring current self-
reported smoking status was identical to the item used in the
ASSB, described above. Additional items on the SSSBQ
included (a) readiness to quit; (b) smoking point prevalence
(24 hours, 7 days, and 30 days); (c) number of cigarettes
smoked per day; (d) use of other forms of tobacco; (e)
environmental smoke exposure; (f) use of nicotine replacement
therapy (NRT); and (g) employment-related tobacco exposure
(i.e., handling tobacco).
Biochemical Validation. To assess the validity of self-reported
smoking, urine samples were collected from participants and
immediately analyzed using the NicAlert strip (Nymox) for
urinary cotinine levels. The NicAlert testing system provides a
semiquantitative measure of cotinine in urine for the purpose
of determining if an individual has been exposed to tobacco
products, such as cigarettes, pipes, or chewing tobacco within
the past 48 hours. NicAlert test strip zones range from zone 0
(0-10 ng/mL, nonsmoker) through zone 6 (>10,000 ng/mL,
a very heavy smoker). The cut point concentration for the
NicAlert test indicating a positive result is 100 ng/mL (zones
3-6). From each participant, f25 mL of a midstream sample of
urine were collected. Urinary cotinine level was recorded by
dipping the NicAlert strip for 20 seconds in the urine sample
to a depth of 0.5 inch while holding the strip with gloves.
Results were read after allowing the strip to develop by laying
the strip on a nonabsorbent surface for 10 to 15 minutes. The
lowest numbered zone displaying a red color was documented
as the NicAlert test result. Consistent with the 100 ng/mL cut
point, participants with outcomes in zone 2 (30-100 ng/mL) or
below were considered negative and classified as nonsmokers.
Data Analysis. As recommended in reviews of this literature
(12, 15), two contingency tables were formed: (a) comparison of
self-reported smoking status measured with the ASSB versus
the SSSBQ and (b) comparison of self-reported smoking status
with classifications obtained with NicAlert test results. Overall
agreement between ASSB and SSSBQ self-reported smoking
status was assessed using kappa statistics, which provide a
measure of concordance corrected for chance. (Kappa statistics
near 1.0 suggest very high levels of agreement.) Sensitivity and
specificity of self-reported smoking status were calculated
using classification by cotinine levels as the ‘‘gold standard.’’
Overall classification rates were also assessed. Data were
reviewed for alternative sources of nicotine exposure in cases
yielding false-positive and false-negative results.
Results
Sample Demographic Characteristics. Participants’ mean
age was 59 years (SD = 8.4, range = 43-73). The majority of
participants were Caucasian (95%, n= 52), male (55%, n= 30),
and in the spiral computed tomography arm of the JH-LCSS
(67%, n= 37). Most participants (73%, n= 40) were in the third
year of screening, with the remainder split evenly between the
second and fourth years.
The 55 participants in the substudy did not differ from the
49 eligible but unenrolled parent study participants on any
measured characteristics (i.e., age, sex, race, study arm,
smoking status, pack-years, or length of participation in parent
study). Compared with the full sample of parent study
participants, the 55 substudy participants were highly similar
in all characteristics except study arm (P< 0.05). This finding is
related to higher screening adherence rates within the
computed tomography group. These comparisons suggest that
the subsample used for this study was representative of the
larger sample of high-risk screening participants.
Self-reported Smoking Behavior: SSSBQ. See Table 1 for a
thorough summary of self-reported smoking behaviors from
the SSSBQ. Three participants (6%) reported having quit
smoking within the prior 6 months, whereas 36% (n= 20)
1826 Validity of Self-reported Smoking and Lung Cancer Screening
Cancer Epidemiol Biomarkers Prev 2006;15(10). October 2006
on May 15, 2017. © 2006 American Association for Cancer Research. cebp.aacrjournals.org Downloaded from

reported having quit >6 months ago. Current smokers
reported smoking between 1 and 50 cigarettes per day, with
a median of 16.
Self-reported Smoking Status: SSSBQ versus ASSB.
Smoking status reports on the ASSB (completed before
substudy participation) and the SSSBQ (completed after being
informed of the purpose of the substudy) were perfectly
consistent. No discrepancies were noted between the self-report
items on the two measures. Because results were identical, only
data from the SSSBQ were used for the remainder of analyses.
Smoking Status: Urinary Cotinine versus SSSBQ Self-
report. See Table 2 for the initial classification results
comparing self-report and urinary cotinine measures of
smoking status. The sensitivity and specificity of self-
reported smoking status were 91% and 95%, respectively
(j= 0.85, P< 0.001, 95% confidence interval = 0.71-0.99).
The total misclassification rate was 7%: three participants
who reported negative smoking status were classified as
smokers by their urinary cotinine levels, and one participant
who reported positive smoking status was classified as a
nonsmoker by the urinary cotinine test. Further exploration
of the data revealed that the three participants with positive
test results but negative self-reports all reported concurrent
use of NRT. Eliminating these cases from the analysis
resulted in self-report sensitivity of 100% and specificity
of 95% (j= 0.96, P< 0.001, 95% confidence interval =
0.88-1.00). These results are depicted in Table 3. Review of
questionnaire responses revealed that the remaining mis-
classified case self-reported very infrequent tobacco use, but
still self-identified as a current smoker; this participant’s
urinary cotinine level (zone 1 = 11-29 ng/mL) was below the
cut point and resulted in classification as a nonsmoker via
the biochemical measure.
Discussion
In this study of participants in a randomized controlled trial of
lung cancer screening, self-reported smoking status was
compared with biochemical verification using urinary cotinine
levels measured with the NicAlert test strip (Nymox). Results
showed strong concordance between self-reported smoking
status and the urinary cotinine measure.
Previous studies have shown that discrepancies between
self-reported smoking status and biochemical verification are
minimal among the general population (15, 19). However,
increased demand characteristics are associated with under-
reporting of smoking in certain populations and contexts,
leading to recommendations of biochemical validation in
studies of smoking cessation among such populations (16).
Participants in lung cancer screening are similar to these
‘‘special groups’’ in that they have histories of smoking, are
likely to have other smoking-related illnesses, and are in
contact with medical professionals for early detection of
disease directly related to smoking history. Therefore, the
lung cancer screening context may constitute a high-demand
situation in which the veracity of self-reported smoking status
may be in question. No previous studies exploring associations
between lung cancer screening participation and smoking
behavior have used the highly sensitive and specific method of
cotinine testing for biochemical validation.
Results of the current study indicated that self-reported
smoking behavior among participants in a randomized trial of
lung cancer screening exhibited a high level of agreement with
smoking status ascertained by test strips measuring urinary
cotinine levels. The sensitivity of self-reported smoking status
measured against biochemical verification ranged from 91% to
100%. Specificity ranged from 95% to 100%.
An important issue arose regarding assessment for use of
NRT when using cotinine screening to validate smoking status.
As cautioned in several reviews of the utility of cotinine
screening (15, 16), use of NRT in a nonsmoking individual can
raise levels of cotinine beyond the threshold for categorization
as a smoker. In this study, three cases were initially
misclassified as smokers due to increased cotinine levels
secondary to NRT. Although carbon monoxide monitoring in
general is a less sensitive and specific measure of smoking
(10, 16), it does have an advantage in that use of NRT does not
trigger erroneous positive test results. Consideration of NRT
use in this investigation allowed a reduction of the original
overall misclassification rate from 7% to 2%. This example
highlights the need for attention to NRT use when using
cotinine testing methods to validate self-reported smoking
status biochemically (16).
Access to participants’ previous responses to questionnaires
in the parent study allowed comparison of self-reported
smokingstatusontwomeasures:oneobtainedbefore
participation in the substudy and one obtained after partic-
ipants were informed of the biochemical verification compo-
nent of the substudy. The two separate self-reports of smoking
behavior (ASSB and SSSBQ, completed before and during
substudy participation, respectively) were perfectly consistent,
providing further support for the veracity and reliability of
self-reported smoking status in this population.
These findings suggest that extensive use of biochemical
verification of smoking status may not be necessary in this
population. Validity of self-reported smoking status was
supported with a high-risk sample who may have been
motivated to underreport smoking. This result is consistent
with findings of high concordance rates in population-based
Table 2. Initial classification table: SSSBQ self-reported
smoking status and urinary cotinine test results
SSSBQ self-reported
smoking status
Urinary cotinine test result Total (N= 55)
Positive Negative
Positive 31 1 32
Negative 3 20 23
Total 34 21
NOTE: Using urinary cotinine as the gold standard, self-reported smoking status
had sensitivity of 91% and specificity of 95% (j= 0.85, P< 0.001, 95% confidence
interval = 0.71-0.99). Assuming smoking prevalence in the lung cancer screening
population was represented in this sample, the positive predictive value of self-
report was 97%, and the negative predictive value was 87%.
Table 1. SSSBQ: self-reported smoking behavior
Smoking behavior Smoking status Total (N= 55)
Current (n= 32) Former (n= 23)
Intentions to quit
using tobacco
Within 30 d 9 — 9
Within 6 mo 15 — 15
None 8 — 8
Use of tobacco other
than cigarettes
Cigars 3 — 3
Other 1 — 1
Use of NRT
Gum 1 1 2
Patch 1 0 1
Lozenge 0 2 2
Other 1 0 1
Second-hand
smoke exposure
Yes 21 7 28
No 11 16 27
NOTE: Second-hand smoke exposure refers to self-reported exposure to second-
hand smoke within the prior 24-hour period.
Cancer Epidemiology, Biomarkers & Prevention 1827
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studies (15, 19) and in a prior lung cancer screening study
using a different biochemical measurement approach (9).
Lung cancer screening may not constitute a high-demand
situation, even for participants at high-risk for lung cancer
and other smoking-related illnesses. Although increased
cessation rates have been reported among lung cancer
screening participants (6-9), the lack of planned cessation
intervention components in most screening programs
may diminish any demand characteristics typically asso-
ciated with medical interventions for tobacco-related con-
ditions (16).
Limitations. The study had several limitations, which
should be considered when interpreting results. First, the
sample was relatively small, consisting of 55 of the 813
participants from the parent study of lung cancer screening. In
addition, a convenience sample of consecutive participants
was used, rather than a random sample of participants from
the parent study. This substudy was initially planned for a
later phase of the JH-LCSS (26). However, early closure of the
screening component of the parent study limited opportunities
for participant accrual to those scheduled for annual screening
in the final month. The study was conducted in Kentucky,
which has the highest prevalence of adult smoking in the
United States (27). It is possible that lung cancer screening
participants in Kentucky are less likely to misrepresent
smoking status than screening participants in other regions.
The high prevalence of smoking in the state may reduce the
social and cultural pressure typically associated with high-
demand situations. Investigations in additional geographic
regions may elucidate whether this lack of misrepresentation is
similar in other areas. Finally, participation in the JH-LCSS
parent study may have increased the likelihood of accurate
self-report among study participants, who were followed for
several years and completed multiple annual self-report
questionnaires addressing smoking behavior. Future studies
could focus on newly recruited participants entering screening
trials to provide additional information about the validity of
self-reported smoking status among lung cancer screening
participants.
Conclusions. In conclusion, self-reported smoking status
and biochemical validation measured via urinary cotinine
levels were highly concordant among a high-risk sample of
participants in a lung cancer screening trial. Self-report data on
smoking status may be used with reasonable confidence in
further investigations of the psychological and behavioral
correlates of participation in lung cancer screening. Given the
validity of self-reported smoking status, future analyses will
explore possible changes in smoking behavior associated with
participation in a randomized clinical trial of lung cancer
screening.
Acknowledgments
We thank Laura Brenzel and the Jewish Hospital Health Care Services
for their assistance and collaboration in conducting this research.
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Table 3. Revised classification table: excluding three cases
due to NRT
SSSBQ self-reported
smoking status
Urinary cotinine test result Total (N= 52)
Positive Negative
Positive 31 1 32
Negative 0 20 20
Total 31 21
NOTE: Using urinary cotinine as the gold standard, self-reported smoking status
had sensitivity of 100% and specificity of 95% (j= 0.96, P< 0.001, 95%
confidence interval = 0.88-1.00). Assuming smoking prevalence in the lung
cancer screening population was represented in this sample, the positive
predictive value of self-report was 97%, and the negative predictive value was
100%.
1828 Validity of Self-reported Smoking and Lung Cancer Screening
Cancer Epidemiol Biomarkers Prev 2006;15(10). October 2006
on May 15, 2017. © 2006 American Association for Cancer Research. cebp.aacrjournals.org Downloaded from

2006;15:1825-1828. Cancer Epidemiol Biomarkers Prev
Jamie L. Studts, Sameer R. Ghate, Jaime L. Gill, et al.
in a Lung Cancer Screening Trial
Validity of Self-reported Smoking Status among Participants
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