Association between preference-based health-related quality of life and asthma severity

Background: Preference-based measures of health-related quality of life (HRQL) focus on choice and strength of preference for health outcomes. If the value people attach to the health improvement they receive from medical treatments for asthma is known, preference-based measures can be used in cost-effectiveness analyses to aid resource allocation decisions. International guidelines have been developed to guide medical management according to asthma severity defined by lung function and symptom frequency. Objective: To test the hypothesis that preferences correlate with asthma severity and that the relationships vary among the preference instruments used and the components of asthma severity studied. Methods: Preferences for subjects' health states were measured using (1) a rating scale (RS), (2) standard gamble (SG), (3) time tradeoff (TTO), (4) Health Utilities Index 3 (HU13), and (5) Asthma Symptom Utility Index (ASUI). We measured level of airways obstruction by forced expiratory volume in I second (FEV1) and symptom frequency of cough, wheeze, dyspnea, and nighttime awakening. Asthma severity was defined by either percentage of predicted FEV1 or symptom frequency. Results: One hundred adults with asthma were studied. Preference scores were lowest for the HU13 (mean, 0.57) and highest for the SG (mean, 0.91). Spearman correlations showed that the strength of the relationship between preference scores and percentage of predicted FEV1 was weak to moderate (r = 0.14-0.36). One-way analysis of variance showed that RS, TTO, and ASUI scores were significantly associated with the percentage of predicted FEV1 (P less than or equal to .01). Both RS and HU13 scores were significantly associated with frequency of all symptoms (P < .05). Conclusions: Preference-based measures of HRQL are correlated with asthma severity defined by lung function or symptoms. The RS was significantly associated with level of airways obstruction and all 4 symptoms evaluated, whereas the SG was not correlated with either marker of asthma severity.