Background/Purpose: 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. The objective is To develop a measure to assess the overall impact of AS on health based on the ICF Core Set for ankylosing spondylitis (add the ref) which can be considered as the external standard of categories that are relevant and typical for AS and contains categories within the bio-medical as well as contextual part of the ICF model for health.

Methods:

Development is being performed in five phases.I development of an item pool using categories of the ICF Core Set for AS as the domain structure; II Item exploration based on Rasch analyses for the items fitting the bio-medical categories and correlation analyses for the contextual factors; III – Agreement on item reduction ; IV  Validation of the draft version; V Agreement on a final version

Table 1: Phases of development for the ASAS Health Index

	Phase	Objectives	Methods
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	Factor Analysis, Rasch Analysis, Spearman rank correlation coefficient
III	Expert consultation	Agreement on item reduction	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	Nominal Consensus Process

Results:

Phase 1: The item pool contained 251 items in 44 categories. It was formed 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 factorspart 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). Phase iV: The draft version are being tested in a 2^ndcross sectional survey. Rasch analysis will help to choose those items which represents the full spectrum of functioning

Conclusion:

The item pool has been successfully reduced 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.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/development-of-a-health-index-for-patients-with-ankylosing-spondylitis-first-steps-of-a-global-initiative-based-on-the-icf-guided-by-asas/