Health-related quality of life in asthma studies. Can we combine data from different countries?

The aim was to compare health-related quality of life (HRQL) in patients with asthma from 4 countries, and to investigate the correlations between HRQL and clinical indices.341 patients; 140 (Sweden), 54 (Norway), 65 (the Netherlands) and 82 (Greece) were treated with formoterol fumarate 4.5 microg or with terbutaline sulphate 0.5mg for 12 weeks inhaled 'on demand' via Turbuhaler. The Asthma Quality of Life Questionnaire (AQLQ) and clinical indices were assessed. The mean baseline AQLQ overall scores in Sweden (4.97), in the Netherlands (5.04), in Norway (4.68) and in Greece (4.68) were in the same range, however, with a significant difference between the four countries (p=0.038). When comparing AQLQ, activity limitation and symptoms domains, the differences between the countries were not statistically significant. The cross-sectional correlations between AQLQ overall score and the clinical indices were similar in all four countries. The magnitude of change in AQLQ was consistent with the other clinical variables. The correlations between change in AQLQ overall score and change in clinical indices were low to medium in all countries. In conclusion, the consistency of cross-sectional correlations between the AQLQ overall and clinical indices across countries supports the validity of translations of the AQLQ used in this study. There were differences in baseline values between the countries. The treatment response in AQLQ differed to the same extent as other clinical indices. When combining HRQL data from different countries, there might be cultural, gender and socio-economic differences, explaining different responses to treatment.