1 Butler-Dawson J, et al. BMJ Open 2021;11:e050374. doi:10.1136/bmjopen-2021-050374 Open access Cross-sectional study examining the accuracy of self-reported smoking status as compared to urinary cotinine levels among workers at risk for chronic kidney disease of unknown origin in Guatemala Jaime Butler-Dawson , 1,2 Joaquin Barnoya, 3,4 Stephen Brindley, 1 Lyndsay Krisher, 1,2 Wenyi Fan, 2 Claudia Asensio, 5 Lee S Newman 1,2,6 To cite: Butler-Dawson J, Barnoya J, Brindley S, et al. Cross-sectional study examining the accuracy of self-reported smoking status as compared to urinary cotinine levels among workers at risk for chronic kidney disease of unknown origin in Guatemala. BMJ Open 2021;11:e050374. doi:10.1136/ bmjopen-2021-050374 ► Prepublication history for this paper is available online. To view these fles, please visit the journal online (http://dx.doi. org/10.1136/bmjopen-2021- 050374). Received 17 February 2021 Accepted 06 October 2021 For numbered affliations see end of article. Correspondence to Dr Jaime Butler-Dawson; jaime.butler-dawson@ cuanschutz.edu Original research © Author(s) (or their employer(s)) 2021. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ. ABSTRACT Objectives There is a lack of information on cotinine levels in rural populations in low-income and middle- income countries like Guatemala. Therefore, there is a need to explore smoking status and biomarkers of tobacco use in epidemiological research in rural, low-income populations, in particular those at-risk for chronic kidney disease of unknown origin (CKDu). Design We evaluated self-reported smoking status against urinary cotinine levels, the gold standard biomarker of tobacco smoke exposure, among agricultural workers at four separate cross-sectional time points. Setting Guatemala. Participants 283 sugarcane workers. Primary outcome measures Compared self-reported smoking status and urinary cotinine levels in two agricultural worker studies. Results Self-reported smoking prevalence was 12% among workers. According to cotinine levels (≥50 ng/ mL), the smoking prevalence was 34%. Self-reported smoking status had 28% sensitivity and 96% specifcity. Urinary cotinine levels show that smoking prevalence is underestimated in this worker population. Conclusions According to our fndings, smoking status should be objectively measured with biomarkers rather than self-reported in CKDu epidemiological research. Self-reported smoking status is likely an underestimate of the true smoking prevalence among agricultural workers. Research on the CKDu epidemic in Central America and other parts of the world might be underestimating tobacco exposure as a potential contributor to the development of CKDu. INTRODUCTION Smoking as a potential contributor to the development of chronic kidney disease of unknown origin (CKDu) has not been fully explored and is often overlooked in CKDu research. The emerging CKDu epidemic has been documented over the past two decades throughout Latin America, Sri Lanka and India. 1 CKDu is not associated with estab- lished CKD risk factors such as diabetes or hypertension and the aetiology remains unknown. 1 Several CKDu risk factors have been proposed, including heat stress, dehy- dration, environmental exposures, infectious agents, medications, as well as a multifactorial aetiology. 1–6 Smoking, as opposed to other CKD risk factors, has received less attention in epide- miological studies in populations at risk for CKDu despite the evidence of its role with CKD. Scientific literature provides both mechanistic and epidemiological evidence linking smoking to kidney disease and it is an established and independent CKD risk factor. 7–9 While few studies have found an association between self-reported smoking and CKDu, 10–13 there may be multiple reasons for the lack of association findings. First, tobacco use misclassification is common and there is considerable heterogeneity between Strengths and limitations of this study ► The study provides an international view of the im- portance of adequately assessing smoking preva- lence by validating the accuracy of self-reported smoking questionnaires. ► The misclassifcation bias of smokers needs to be examined in rural populations. ► Urine cotinine and self-reported smoking status were investigated concurrently at multiple cross- sectional time points. ► The study results may have limited generalisability as it was conducted among agricultural workers in Guatemala. on April 13, 2022 by guest. Protected by copyright. http://bmjopen.bmj.com/ BMJ Open: first published as 10.1136/bmjopen-2021-050374 on 25 October 2021. Downloaded from