ObjectivesWe hypothesised that chronic obstructive pulmonary disease (COPD)-specific health status measured by the COPD assessment test (CAT), respiratory symptoms by the evaluating respiratory symptoms in COPD (E-RS) and dyspnoea by Dyspnoea-12 (D-12) are independently based on specific conceptual frameworks and are not interchangeable. We aimed to discover whether health status, dyspnoea or respiratory symptoms could be related to smoking status and airflow limitation in a working population.DesignThis is an observational, cross-sectional study.Participants1566 healthy industrial workers were analysed.ResultsRelationships between D-12, CAT and E-RS total were statistically significant but weak (Spearman’s correlation coefficient=0.274 to 0.446). In 646 healthy non-smoking subjects, as the reference scores for healthy non-smoking subjects, that is, upper threshold, the bootstrap 95th percentile values were 1.00 for D-12, 9.88 for CAT and 4.44 for E-RS. Of the 1566 workers, 85 (5.4%) were diagnosed with COPD using the fixed ratio of the forced expiratory volume in one second/forced vital capacity <0.7, and 34 (2.2%) using the lower limit of normal. The CAT and E-RS total were significantly worse in non-COPD smokers and subjects with COPD than non-COPD never smokers, although the D-12 was not as sensitive. There were no significant differences between non-COPD smokers and subjects with COPD on any of the measures.ConclusionsAssessment of health status and respiratory symptoms would be preferable to dyspnoea in view of smoking status and airflow limitation in a working population. However, these patient-reported measures were inadequate in differentiating between smokers and subjects with COPD identified by spirometry.

IntroductionIt has been emphasized that spirometry is essential in making a diagnosis of chronic obstructive pulmonary disease (COPD) since COPD is defined by airflow limitation measured using spirometry [1]. However, COPD remains under-diagnosed, with the diagnosis being commonly missed or delayed until the disease is advanced. Since COPD screening by spirometry may be a little expensive, the concept of case-identification or case-finding to pre-select candidates for spirometry has been proposed [2,3] and the possibility of identifying people at high risk for COPD has been studied. So far, two presumptive methods have been reported for target case identification to reduce the burden of COPD. One method uses a portable device called a handheld spirometer instead of a conventional spirometer [4], and the other is a screening method using specific questionnaires [2,5]. Researchers have also been investigating the discriminative properties of various biomarkers; however, there is still no known biomarker useful for diagnosing or screening COPD.Although vitamin D is not a biomarker, there have been some studies to determine whether vitamin D plays a role in some respiratory diseases. An association between vitamin D deficiency and decreased pulmonary functions as well as airflow limitation in asthma patients has been suggested [6]. There have been some reports of the possible association of acute exacerbation of COPD with vitamin D deficiency although there have also been other reports that no association exists [7,8]. Martineau et al.