The Effect of Area-Level Socioeconomic Status on Disease Outcomes in Rheumatoid Arthritis: Results From an Australian Longitudinal Inception Cohort Study.

Abstract

Socioeconomic status (SES) is associated with differences in health outcomes for individuals with rheumatoid arthritis (RA). We aimed to determine the effect of area-level SES on RA disease activity, disability, quality of life (QOL), and biologic/targeted synthetic disease-modifying antirheumatic drug (b/tsDMARD) use in individuals with early RA managed within a protocolized, treat-to-target (T2T), longitudinal observational cohort study. Adult patients with RA diagnosed after June 2003 were included. SES was defined as quintiles of Index of Relative Social Advantage and Disadvantage (IRSAD) based on residential address at baseline. Covariates included baseline age, sex, smoking status, BMI, and the Rheumatic Disease Comorbidity Index (RDCI). Longitudinal multivariable random effects regression models were constructed with restricted cubic splines examining nonlinear responses in outcome variables. b/tsDMARD use was examined using time-to-event models for recurrent events. Of 255 participants, 66.7% were female, with mean age 53.9 years, and 68% had seropositive disease. There was an ordered trend across SES quintiles, such that higher quintiles were associated with lower Disease Activity Score in 28 joints based on C-reactive Protein (DAS28-CRP; <i>P</i> = 0.03), lower modified Health Assessment Questionnaire (mHAQ; <i>P</i> = 0.001), and higher 36-item Short Form Health Survey physical component summary (SF-36 PCS; <i>P</i> < 0.001). SES quintile was not significantly associated with b/tsDMARD initiation or switching. Disadvantageous SES was associated with higher disease activity, disability, and poorer QOL. Our results suggest an inequity in health outcomes for patients with RA despite T2T management within a universal healthcare system.