title: Estimation of health-related utility (EQ-5D index) in subjects with seasonal allergic rhinoconjunctivitis to evaluate health gain associated with sublingual grass allergen immunotherapy.
abstract: BACKGROUND
  Grass allergen immunotherapy (AIT) reduces symptom severity in seasonal allergic rhinoconjunctivitis (ARC) but its impact on general health-related utility has not been characterised for the purposes of economic evaluation. The aim of this study was to model the preferred measure of utility, EQ-5D index, from symptom severity and estimate incremental quality adjusted life years (QALYs) associated with SQ-standardised grass immunotherapy tablet (GRAZAX®, 75,000 SQ-T/2,800 BAU, ALK, Denmark).
  
  
  METHODS
  Data were analysed from five consecutive pollen seasons in a randomised placebo controlled trial of GRAZAX®. Binomial and Gaussian mixed effects modelling related weekly EQ-5D index score to daily symptom and medication scores (DSS & DMS respectively). In turn, daily EQ-5D index was estimated from ARC symptoms and medication use.
  
  
  RESULTS
  DSS and DMS were the principal predictors of 'perfect' health (EQ-5D = 1.000; binomial) and 'imperfect' health (EQ-5D < 1.000; Gaussian). Each unit increase in DSS and DMS reduced the odds of 'perfect' health (EQ-5D = 1.000) by 27% and 16% respectively, and reduced 'imperfect' health by 0.17 and 0.13, respectively. Gender remained the only other significant main fixed effect (Male odds ratio [OR] = 1.82). Incremental estimated EQ-5D index utility for GRAZAX® was observed from day -30 to day +70 of the pooled pollen season; mean daily utility for GRAZAX® = 0.938 units (95%CI 0.932-0.943) vs. 0.914 (0.907-0.921) for placebo, an incremental difference of 0.0238 (p < 0.001). This translates into an incremental 0.0324 Quality Adjusted Life Years over the five year study period.
  
  
  CONCLUSIONS
  ARC symptoms and medication use are the main predictors of EQ-5D index. The incremental QALYs observed for GRAZAX® may not fully describe the health benefits of this treatment, suggesting that economic modelling may be conservative.
authors.forename: Chris D
authors.initials: CD
authors.lastname: Poole
authors.forename: Christian A
authors.initials: CA
authors.lastname: Bannister
authors.forename: Jakob Nørgaard
authors.initials: JN
authors.lastname: Andreasen
authors.forename: Jens Strodl
authors.initials: JS
authors.lastname: Andersen
authors.affiliation: Cochrane Institute of Primary Care and Public Health, Cardiff University, Cardiff, Wales, UK. currie@cardiff.ac.uk.
authors.forename: Craig J
authors.initials: CJ
authors.lastname: Currie
mesh_terms: D000286:Administration, Sublingual; D000328:Adult; D000485:Allergens; D003233:Conjunctivitis, Allergic / Q000188:drug therapy* / Q000191:economics / Q000503:physiopathology*; D003888:Desensitization, Immunologic; D005260:Female; D006801:Humans; D008297:Male; D010936:Plant Extracts / Q000627:therapeutic use*; D006109:Poaceae; D011058:Pollen; D019057:Quality-Adjusted Life Years; D016032:Randomized Controlled Trials as Topic; D012015:Reference Standards; D006255:Rhinitis, Allergic, Seasonal / Q000188:drug therapy* / Q000191:economics / Q000503:physiopathology*; D013607:Tablets; D016896:Treatment Outcome
chemical_list: D000485:Allergens; C551013:Grazax; D010936:Plant Extracts; D013607:Tablets