While systemic lupus erythematosus and lupus nephritis (LN) disproportionately affect females, previous studies suggest that males may experience poorer outcomes. We undertook this study to investigate sex differences in health care utilization, end-stage renal disease (ESRD), and mortality among patients with LN receiving Medicaid, public insurance for low-income individuals.
Within the Medicaid Analytic eXtract (MAX) from 29 states (from 2000 to 2010), we used billing claims to identify individuals ages 5-65 years with incident LN (positive predictive value 80%). MAX data were linked to the US Renal Data System to determine ESRD and to Social Security Death Index files to determine death. We estimated adjusted incidence rate ratios (IRRs) by sex for health care utilization using Poisson regression, and we used multivariable proportional hazards models to compare risks of ESRD and death by sex.
Of 2,750 patients with incident LN, 283 (10%) were male. The mean ± SD follow-up period for both sexes was 3.1 ± 2.3 years. The mean ± SD age was 29.6 ± 13.9 years among females and 24.7 ± 14.1 years among males (P < 0.01). Males had fewer outpatient visits (IRR 0.88 [95% confidence interval (95% CI) 0.80-0.97]) and fewer emergency department visits (IRR 0.75 [95% CI 0.63-0.90]). The 5-year cumulative incidence of ESRD was 22.3% in males and 21.2% in females. The 5-year cumulative incidence of death was 9.4% in males and 9.8% in females. Comparing males to females, there were no sex differences in ESRD (subdistribution hazard ratio [HR] 1.05 [95% CI 0.76-1.45]) or death (HR 0.81 [95% CI 0.47-1.35]).
In this cohort of patients with incident LN, ESRD and mortality were extremely high overall but were not increased among males compared to females. In this vulnerable population, biologic and health care utilization differences by sex may not significantly affect outcomes.