Does SLE widen or narrow race/ethnic disparities in the risk of five co-morbid conditions? Evidence from a community-based outpatient care system.

OBJECTIVE: The heterogeneous spectrum of systemic lupus erythematosus (SLE) often presents with secondary complications such as cardiovascular disease (CVD), infections and neoplasms. Our study assessed whether the presence of SLE independently increases or reduces the disparities, accounting for the already higher risk of these outcomes among racial/ethnic minority groups without SLE.

METHODS: We defined a cohort using electronic health records data (2005-2016) from a mixed-payer community-based outpatient setting in California serving patients of diverse racial/ethnic backgrounds. The eligible population included adult patients with SLE and matched non-SLE patients (≥18 years old). SLE was the primary exposure. The following outcomes were identified: pneumonia, other infections, CVD and neoplasms. For each racial/ethnic group, we calculated the proportion of incident co-morbidities by SLE exposure, followed by logistic regression for each outcome with SLE as the exposure. We evaluated interaction on the additive and multiplicative scales by calculating the relative excess risk due to interaction and estimating the cross-product term in each model.

RESULTS: We identified 1036 SLE cases and 8875 controls. The incidence for all outcomes was higher among the SLE exposed. We found little difference in the odds of the outcomes associated with SLE across racial/ethnic groups, even after multivariable adjustment. This finding was consistent on the multiplicative and additive scales.

CONCLUSION: We demonstrated that SLE status does not independently confer substantial interaction or heterogeneity by race/ethnicity toward the risk of pneumonia, other infections, CVD or neoplasms. Further studies in larger datasets are necessary to validate this novel finding.