Background The burden of ankylosing spondylitis (AS) can be considerable. The patients suffer from pain, stiffness and fatigue, and they are limited in their activities and restricted in social participation. The International Classification of Functioning, Disability and Health (ICF), a model to systematically classify and describe functioning, disability and health in human beings, has been used by the Assessments of SpondyloArthritis international Society (ASAS) as a basis to define a core set of items that are typical and relevant for patients with AS. However, no ICF-based patient-reported outcome measure has been developed for AS patients.
Objectives To develop a measure to assess the burden of AS, the AS Health Index, based on the Comprehensive ICF Core Set for AS.
Methods Development of this health index is being performed in five phases.
I. Preparatory: Development of a pool of items representing the categories of the Comprehensive ICF Core Set, Linkage of various assessment tools for functioning and health to ICF categories
II. 1st postal patient survey: Item reduction with Factor Analysis, Rasch Analysis, Spearman rank correlation coefficient
III. Expert consultation: Agreement on item reduction with Nominal Consensus Process
IV. 2nd postal patient survey: Validation of the draft version and further item reduction, Testing psychometric properties, Rasch Analysis
V. Consensus Meeting: Agreement on a final version with Nominal Consensus Process
Results The first three phases have been completed. During the preparatory phase (Phase 1): a pool of 251 items in 44 categories was collected from various instruments (identified through literature search) which focus on symptoms and functioning in patients with AS. Phase 2: An international cross sectional study with 1915 AS patients (mean age 51.2±3.6, 53% male, BASDAI 5.5±2.4) was conducted in 4 continents. In 82 items of the functioning part a unidimensional scale, fit to the Rasch model and absence of Differential Item Function could be confirmed. 32 items of the environmental factors part showed a significant correlation between person score and ICF category (correlation coefficient between 0.04 - 0.45). Phase 3: Based on results of the analyses in step 2, an expert committee selected 50 functioning items and 16 environmental factor items using predefined selection criteria (clinimetric properties, ease of wording, coverage of the whole range of ability).
Conclusions The item pool has been successfully reduced from 251 down to 66 items. In covering much of the ICF Core Set for AS, these items represent a whole range of abilities of patients with AS. This draft version will be tested in a second survey to create a first version of the ASAS Health Index. The final measure can be used in clinical trials and cohort studies as a new composite index that captures relevant information on the health status of the patients.
Disclosure of Interest None Declared
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