Validation of global item for assessing impact on quality of life of patients with hidradenitis suppurativa

Background Hidradenitis suppurativa (HS) is a chronic inflammatory disease. The HS core outcome set calls for a patient global assessment (PtGA). Objectives To assess the validity, reliability and responsiveness of a candidate single‐item PtGA for HS‐specific health‐related quality of life (HRQoL). Methods Cognitive debriefing interviews were conducted with patients with HS in Denmark and the USA. A cross‐sectional observational study was done with adults with HS in the USA and Denmark. Candidate PtGA item, demographic items and multiple patient‐reported scales – the Hidradenitis Suppurativa Quality of Life (HiSQOL), Dermatology Life Quality Index (DLQI) and numerical rating scale (NRS) for pain – were concurrently administered to evaluate convergent and known‐groups validity. Scales with a single‐item assessment of change were readministered 24–72 h later, to evaluate reliability and responsiveness. Results After cognitive debriefing, the candidate PtGA for HS‐specific HRQoL was finalized with five response levels. Convergent validity of the PtGA was supported by significant correlations with HiSQOL score [r = 0·79, 95% confidence interval (CI) 0·75–0·82] and DLQI (r = 0·78, 95% CI 0·74–0·82). The PtGA displayed known‐groups validity with DLQI score bands based on significance of an anova (P