213 Low-dose-CT versus X-ray in patients suspected of pulmonary disease treatment, hospital admission and discharge were at the discretion of the attending physician, according to national guidelines, if applicable. Data collection Baseline ED data included medical history and physical examination, laboratory, microbiological and radiological test results, diagnosis at ED discharge, prescription of antibiotics or diuretics, and hospital admission. Follow-up data after ED discharge included disease course, treatment outcome, additional imaging, hospital length of stay, mortality up to day 28, and patients in follow-up after day 28 because of incidental findings. All data were obtained from electronic patient records. Whenever necessary, additional information was obtained from general practitioners, nursing wards, outpatient clinics, or hospitals where patients had been transferred or referred to. Twenty-eight days after ED presentation study participants received the short form (SF)-12 questionnaire; the questionnaires were available in Dutch and English and in electronic and paper form. We prompted with frequent reminders to ensure maximum response. We assigned one or more final diagnoses after 28 days of follow-up, based on a review of all clinical, radiological and microbiological data available. For this purpose, a diagnostic handbook was developed enabling standardized and reproducible categorization for 32 diagnoses. More details on the methodology of the handbook, its evaluation and validation are available elsewhere [20]. Patients in whom the day 28 diagnosis could be assigned were also assigned an ED discharge diagnosis. All baseline and follow-up data and questionnaires responses were coded and saved in electronic Case Report Forms (Castor EDC, Amsterdam, The Netherlands). Outcomes Considering the wide range of conditions and underlying diagnoses, we selected a generic health-related outcome measure with minimal burden for study participants. The primary outcome was functional health at day 28 after ED presentation, as measured by the physical component summary scale (PCS) score of the SF-12 questionnaire version 1 (scale 0-100, higher score corresponds to better functional health)[21]. Secondary outcomes included hospital admission, hospital length of stay, mortality within 28 days, number of patients requiring follow-up because of incidental findings on ULDCT or CXR after 28 days, and mental health measured by the mental component summary scale (MCS) score of the SF-12 (scale 0-100)[21]. An economic evaluation will be reported elsewhere. Statistical analysis We evaluated all effects in those who underwent the allocated imaging method. We express the effect of imaging as an absolute mean difference in the SF-12 PCS score, with a 95% lower confidence interval. A one-point difference in the mean SF-12 PCS score was defined as the non-inferiority margin. The primary analyses were done using all available data, with sensitivity analyses using multiple imputation of missing questionnaire responses (using age and sex as predictors) and to adjust for confounding. Since we anticipated non-response of the 9
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