Background/Purpose:

Prior studies suggest that males with lupus nephritis (LN) may have worse outcomes than females. However, the majority of these studies, are from tertiary-care centers and there are few large cohort studies of sex differences in LN outcomes. We thus investigated risks of ESRD and death by sex in a nationwide cohort of patients with incident LN.

Methods:

Within the Medicaid Analytic eXtract (MAX) with billing claims from 47 US states and D.C., we identified individuals aged 5-65 with incident LN from 2000-4 using a previously described algorithm (>3 ICD-9 codes for SLE and > 2 codes for acute renal disease all >30 days apart, following > 12 months with none of these codes). MAX data were linked by the Centers for Medicare and Medicaid Studies (CMS) to the US Renal Datasystem (USRDS) to identify ESRD onset and subsequent deaths. The index date was the date that the incident LN definition was met. We followed individuals in the linked dataset through 12/31/2006. Deaths were captured in MAX prior to ESRD and in USRDS after ESRD. We examined baseline sex differences in sociodemographics and SLE comorbidities in the 12 months prior to the index date. We used Fine and Gray proportional hazards models to determine the subdistribution hazard ratios (HR) for ESRD by sex, accounting for the competing risk of death. Multivariable Cox proportional hazards regression models were used to estimate HRs for death by sex. To test the proportional hazards assumption, we included an interaction term for sex and follow-up time. The interaction term was statistically significant in our ESRD model and we therefore stratified follow-up time at <2 vs. >2 years post-index date where survival curves diverged.

Results: Of the 2576 Medicaid patients with incident LN, 230 (9%) were male. Mean age was 30 years (+16) among males and 34 years (+14) among females (p<0.001). More males than females were White (32% vs. 20%), and fewer Black (23% vs. 32%), p 0.02. There was no significant difference in the SLE comorbidity index (p 0.11). Mean follow-up was 2.8 (+1.5) years for both sexes (p 0.62). Among 200 females and 27 males who developed ESRD, median time to ESRD was 1.35 (range 0.11-4.62) years and 2.02 (range 0.11-4.02) years. 216 females and 17 males died in follow-up (including 31 females and 4 males who died after ESRD onset). While the HR for ESRD was similar within 2 years of incident LN, it was significantly elevated among males (HR 2.87, 95%CI 1.48, 5.24) at > 2 years after incident LN. (Table). HR for death did not differ by sex.

Conclusion: ESRD risk was comparable in both sexes within 2 years of LN onset, but higher among males thereafter. Mortality rates were similar in males and females. To our knowledge, this is one of the largest incident LN cohorts followed for long-term outcomes by sex. However, the relatively small number of males limits conclusions. Further study of LN outcomes by sex should be pursued.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/sex-differences-in-rates-of-end-stage-renal-disease-and-death-among-medicaid-patients-with-incident-lupus-nephritis/