Validity of the self-reported smoking status of schizophrenia patients, taking gender-related differences into consideration

Objective. It is unclear whether self-reported smoking status reflects the true smoking status in schizophrenia patients. This study aims to evaluate the consistency in smoking status in schizophrenia patients, as determined using self-reported questionnaires and objective measurements, while considering gender-related differences. Methods. The study involved 158 Japanese schizophrenia patients (79 men and 79 women), who were diagnosed according to DSM-IV-TR criteria. The patients answered questions about their smoking status and daily cigarette consumption. The carbon monoxide (CO) level in the expired air was measured to confirm the self-reported answers. We descriptively analysed the data and assessed the proportion of results showing consistency between the self-reported smoking status and measured CO levels. Results. The self-reported smoking status was consistent with the objective measurement results in both genders. Among the various cut-off CO levels considered, 7 ppm was found to be the optimal level in both men and women. Conclusions. Our study showed that self-reporting is a reliable method for evaluating the smoking status of schizophrenia patients, regardless of gender. However, for precise assessment on the basis of CO levels in expired air, lower cut-off points may be better than the recommended ones.