Background/Purpose: Past studies suggest that males with lupus nephritis
(LN) may have increased rates of end-stage renal disease (ESRD) and mortality
compared to females. Most prior studies have focused on biological differences and few have examined variations in healthcare use and access. We investigated potential sex
differences in healthcare utilization in the period surrounding onset of LN in
a nationwide incident LN cohort.

Methods: We
utilized the Medicaid Analytic eXtract (MAX) with billing claims from 47 U.S.
states and Washington, D.C.to identify children and adults ages 5-65 with
incident LN from 2000-2004. We used a previously validated ICD-9 code algorithm
for LN (PPV 80%), and required 12 months without any LN codes to define
incident cases. MAX data were linked to the US Renal Data System to identify
ESRD onset. The index date was the date the incident LN definition was met and
we followed individuals in both datasets through 2006. Subjects were censored
at death, ESRD, Medicaid disenrollment, or end of follow-up. We evaluated
sociodemographics by sex and calculated sex-specific proportions of SLE and
renal medication use, renal biopsies and preventive care in the period 3 months
prior through 12 months after the index date. We estimated incidence rates of all
emergency department, outpatient, and inpatient visits during this period. We
used Poisson regression models to calculate incidence rate ratios for
healthcare utilization by sex, adjusting for baseline sociodemographic and
clinical characteristics.

Results: Of
2576 patients with incident LN, 230 (9%) were male. Mean follow-up was 2.8 (±1.5)
years for both sexes.  Mean age was
30 years (±16) among males and 34 years (±14) among females
(p<0.001). More males were White (32% vs. 20% of females) and fewer Black
(23% vs. 32%, p 0.02). Geographically, a higher proportion of males lived in
the West (p 0.006) and in higher socioeconomic status areas (p 0.02). There was
no significant difference in the SLE comorbidity index (p 0.11). 31% of men and
37% of women underwent renal biopsy (p 0.06), while 10% of males and 16% of
females received azathioprine (p 0.02). There were no statistically significant
differences by sex in use of immunosuppressives
overall, hydroxychloroquine, glucocorticoids,
angiotensin-converting enzyme inhibitors, angiotensin receptor blockers, erythropoetin, or in influenza or pneumoccocal
vaccine uptake. Incidence rates of inpatient admissions were similar for both
sexes, but the rates of outpatient and emergency department visits were
significantly lower among males (Table).

Conclusion:
In this large incident LN cohort, males had modestly lower rates of outpatient and
emergency department visits than did females. Further studies are needed to
understand whether the observed variation is related to differences in SLE
activity or in health-seeking behavior, and how it relates to long-term
outcomes.