DISCRIMINATIVE ASPECTS OF 2 GENERIC AND 2 ASTHMA-SPECIFIC INSTRUMENTS- RELATION WITH SYMPTOMS, BRONCHODILATOR USE AND LUNG-FUNCTION IN PATIENTS WITH MILD ASTHMA

The objective of this study was to compare the two most frequently use d asthma-specific quality of life (QOL) questionnaires and two generic QOL questionnaires with clinical data in order to establish their abi lity to discriminate in asthma severity, also referred to as cross-sec tional construct validity. We conducted a multicentre, randomized, pla cebo-controlled study investigating the long-term effects of the long- acting beta(2)-agonist formoterol in asthma patients using inhaled cor ticosteroids and short-acting beta(2)-agonists. Before randomization, the peak expiratory flow (PEF) and use of beta(2)-agonists for relief of symptoms were recorded twice daily for 1 month. At the end of the r un-in period, the forced expiratory volume in 1 s (FEV1), airway hyper -responsiveness (PC20, methacholine) and QOL were measured, using two asthma-specific questionnaires, the Asthma Quality of Life Questionnai re (AQLQ) and the Living with Asthma Quality of Life Questionnaire (LW AQ), as well as two generic questionnaires, the Short Form 36 (SF-36) and the Psychological General Well Being (PGWB) index. The quality of life of the patients (n = 110) was only mildly impaired. The mean symp tom score was 3.6 on a scale of 0-21 and the mean FEV1 was 65% of that predicted. The correlations between the QOL parameters and objective measures of asthma severity, such as the FEV1, PEF and PC20, were low (0.01-0.37). The correlations between the QOL parameters and subjectiv e measures of asthma severity, such as symptom scores (range 0.26-0.65 ) and beta(2)-agonist use for the relief of symptoms (0.09-0.39), were higher. The correlations of the activity and symptoms domains of the AQLQ with diary-obtained symptom scores were r = 0.50 (p < 0.0001) and r = 0.65 (p < 0.0001), respectively. The correlation between the phys ical construct of the LWAQ and symptom scores was r = 0.42 (p < 0.001) and that between the physical sumscore of the SF-36 and Symptom score s was r = 0.50 (p < 0.001). The correlation between the PGWB and sympt om scores was r = 0.41 (p < 0.001). The relation between the FEV1, PEF and PC20 and QOL was very low. The QOL measurements related well to t he symptom scores. The AQLQ had a better cross-sectional construct val idity than the LWAQ. The cross-sectional construct validity of the SF- 36 was surprisingly high for this group of patients and the SF-36 perf ormed better than the PGWB and LWAQ.