Association of Poverty Income Ratio with Physical Functioning in a Cohort of Patients with Systemic Lupus Erythematosus

Abstract

Objective.To examine the association of income relative to the poverty threshold [poverty income ratio (PIR)] with self-reported physical functioning (PF) in a cohort of patients with systemic lupus erythematosus.Methods.We used cross-sectional data on 744 participants from Georgians Organized Against Lupus (GOAL), and secondary analyses used data on 56 participants from a nested pilot study. Primary analyses used multivariable linear regression to estimate the association between PIR (categorized as < 1.00, 1.00–1.99, 2.00–3.99, and ≥ 4.00; lower PIR indicate higher poverty) and PF (scaled subscore from the Medical Outcomes Study Short Form–12 survey; range 0–100, higher scores indicate better functioning). Secondary analyses summarized complementary measures of PF as means or percentages by PIR (categorized as < 1.00, 1.00–1.99, and ≥ 2.00).Results.The mean age of participants was 48.0 years; 6.7% were male; 80.9% were black; and 37.5%, 21.0%, 29.6%, and 12.0% had PIR of < 1.00, 1.00–1.99, 2.00–3.99, and ≥ 4.00, respectively. The overall mean PF score was 45.8 (36.2, 40.7, 55.5, and 61.2 for PIR of < 1.00, 1.00–1.99, 2.00–3.99, and ≥ 4.00). With adjustment, higher PIR remained associated with higher PF scores [2.00–3.99 vs 1.00–1.99: β = 10.9 (95% CI 3.3–18.6); ≥ 4.00 vs 1.00–1.99: β = 16.2 (95% CI 6.4–26.0)]. In secondary analyses, higher PIR was also associated with higher scores for objective physical performance.Conclusion.Our results show that higher income relative to the poverty threshold is associated with better PF across multiple domains, warranting further research into multicomponent functional assessments to develop individual treatment plans and potentially improve socioeconomic disparities in outcomes.