[Assessment of urinary cotinine levels in heated tobacco product (HTP) users: Effectiveness of enzyme-linked immunosorbent assay (ELISA)].

Objectives　Urinary cotinine concentration is widely used as a reliable biomarker to objectively evaluate smoking status. High-precision methods, such as liquid chromatography-mass spectrometry (LC-MS) and gas chromatography-mass spectrometry (GC-MS), are mainly used for measuring cotinine concentrations. However, these techniques require expensive equipment and specialized analytical techniques; therefore, they are not suitable for large-scale surveys. Conversely, enzyme-linked immunosorbent assay (ELISA), which is simple and low-cost and has a precision comparable to that of LC-MS and GC-MS, has attracted attention. ELISA has been shown to be useful for evaluating urinary cotinine levels in combustible cigarette smokers; however, its application to heated tobacco product (HTP) users has not yet been examined. Thus, in this study, we aimed to measure urinary cotinine concentrations in HTP users and ascertain whether ELISA is as effective as LC-MS for such measurements.Methods　Urine samples were collected from workers at a certain workplace during lunch breaks on weekdays. In total, 33 participants were analyzed: 11 nonsmokers, 13 cigarette-only smokers, and 9 HTP-only users. Urinary cotinine concentrations were measured using LC-MS and ELISA. The correlation between the measurements obtained using these methods was evaluated using Pearson's correlation coefficient; the agreement was examined using the Bland-Altman analysis.Results　The ELISA and LC-MS results showed a high correlation (cigarette-only smokers: r ＝ 0.84, P ＜ 0.001; HTP-only users: r ＝ 0.96, P ＜ 0.001). The Bland-Altman plot showed a high degree of agreement, with 90.9% of the data between both methods falling within the limits of agreement.Conclusion　ELISA was useful for evaluating urinary cotinine levels in cigarette smokers and HTP users. Because of its convenience and low cost, ELISA is expected to be utilized for large-scale epidemiological surveys and promoting smoking control in workplaces.