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

OBJECTIVE: To examine the association of income relative to the poverty threshold [poverty income ratio (PIR)] with self-reported physical functioning in a cohort of systemic lupus erythematosus patients.

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 utilized 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 PIRs indicate higher poverty) and Physical Functioning (PF; scaled subscore from Short Form-12 survey; range, 0-100, higher scores indicate better functioning). Secondary analyses summarized complementary measures of physical functioning as means or percentages by PIR (categorized as <1.00, 1.00-1.99, and ≥2.00).

RESULTS: Overall, 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 PIRs 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 PIRs of <1.00, 1.00-1.99, 2.00-3.99, and ≥4.00, respectively). With adjustment, higher PIRs remained associated (β (95% CI)) with higher PF scores (2.00-3.99 vs. 1.00-1.99: 10.9 (3.3 to 18.6); ≥4.00 vs. 1.00-1.99: 16.2 (6.4 to 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 physical functioning across multiple domains, warranting further research into multicomponent functional assessments to develop individual treatment plans and, potentially, improve socioeconomic disparities in outcomes.