Possible maximal change in the SF-36 of outpatients with chronic obstructive pulmonary disease and asthma

The purpose of the present study was to investigate the responsiveness of the Short Form-36 (SF-36) in patients with chronic obstructive pulmonary disease (COPD) and asthma. We studied patients with COPD and asthma who attended our outpatient clinic. In the first cross-sectional study, we compared the differences in the SF-36 scores between pretreatment patients (152 with COPD and 174 with asthma) who visited the clinic for the first time and in-treatment patients (123 with COPD and 151 with asthma) who had received treatment for > 6 months. The differences in each scale of the SF-36 ranged from 6.9 to 14.4 in COPD patients and from 7.0 to 28.3 in asthma patients. In the second longitudinal study, patients who visited for the first time were enrolled, and the initial, and, 3-, 6-, and 12-month evaluations of the SF-36 were studied. A total of 136 COPD patients and 136 asthma patients were enrolled consecutively, and 100 patients with COPD and 66 patients with asthma completed the year-long examinations. In COPD patients, except for bodily pain, the scores in all scales of the SF-36 improved significantly during the first 3 or 6 months. In patients with asthma, all scale scores of the SF-36 improved significantly during the first 3 months. Maximal changes in the SF-36 scores were observed at 6 or 12 months. Longitudinal maximal changes in each scale approached or exceeded the possible maximal changes, which were derived from the differences in the scores between pretreatment patients and in-treatment patients in the first cross-sectional study. Improvements in the SF-36 scores showed moderate to strong negative correlations with their baseline scores in patients with COPD and asthma. In conclusion, the SF-36 shows sufficient responsiveness in the assessment of the health status of patients with COPD and asthma, but these responses are strongly influenced by their baseline values.