Physical function is one of the core domains to be measured in all trials in psoriatic arthritis (PsA). We aimed to evaluate two instruments for physical function in PsA: The Health Assessment Questionnaire-disability index (HAQ-DI) and the physical functioning subscale of the Medical Outcome Survey Short-Form 36 items (SF-36 PF).
We followed guidelines set out by the OMERACT Filter 2.1. A working group was formed to evaluate each instrument for domain match and feasibility to reach consensus. Two systematic literature reviews (SLRs) were conducted to identify the relevant articles supporting measurement properties of both instruments. Five additional measurement properties were appraised: construct validity, test-retest reliability, longitudinal construct validity, clinical trial discrimination, and threshold of meaning. New evidence was synthesized to fill the gap. Data were presented to the OMERACT technical advisory group (TAG) and the Group for Research and Assessment of Psoriasis and Psoriatic Arthritis (GRAPPA) community for endorsement.
The results for seven measurement properties for HAQ-DI and SF-36 PF were presented in Summary of Measurement Property (SOMP) tables. The working group proposed "Provisional Endorsement" for both instruments. The body of evidence was approved by the OMERACT TAG. In two Delphi exercises among GRAPPA members, HAQ-DI received 93.9% and 97.5% endorsement votes, while that for SF-36 PF were 86.7% and 77.3%.
Both HAQ-DI and SF-36 PF were provisionally endorsed for the measurement of physical function in PsA trials, using the OMERACT Filter 2.1.