Background/Purpose:

Estimates of the healthcare costs of Granulomatosus with polyangiitis (GPA) and predictors of costs are scarce.  In particular, while socioeconomic status (SES) is associated with costs in general populations, its impact in GPA is unknown.  To address these gaps, we estimated the incremental (extra) direct medical costs of a general population-based cohort of incident GPA for the first five years after diagnosis, and examined the relationship between SES at diagnosis, and medical costs in GPA.

Methods:

Data Source: Our administrative data captured all provincially-funded outpatient encounters and hospitalizations (1990-2010) and all dispensed medications for ALL residents of the province of British Columbia, Canada.

Sample: We assembled a population-based cohort of all cases of GPA who had a new diagnosis of GPA from at least one hospitalization or rheumatologist visit, or two non-rheumatologist visits, between Jan 1996 and Dec 2010, and no prior GPA diagnosis between Jan 1990 and Dec 1995. Ten controls matched by age at diagnosis (±2 years), sex, and calendar year of diagnosis were selected for each case from the general population.  SES was defined from Statistics Canada neighbourhood income quintile data for the year of GPA diagnosis.

Cost Calculation: Outpatient and prescription costs were summed directly from billing data. Case-mix methodology was used for hospitalizations.

Statistical Analysis: We estimated the unadjusted incremental costs of GPA (difference in per-patient-year (PY) costs between cases and controls).  Generalized linear models were then used to:

1. Further adjust for differences in SES, urban/rural residence, and Charlson-Romano comorbidity index between cases and controls; and
2. Evaluate the relationship between SES and direct medical costs among GPA cases.

Results: We matched 441 incident GPA cases to 4,410 controls (54% female, mean age 61 ±16.0 years, median comorbidity score=1). 

Unadjusted incremental costs of GPA for the first 5 years after diagnosis averaged $81,603 per-PY (2010 Canadian), with 80% from hospital, 15% from outpatient, and 5% from medications.  74% of cases (vs. 17% of controls) were hospitalized during the first year after diagnosis, with GPA cases averaging 0.86 more admissions per-PY than controls (excluding the index admission).  Following adjustment, costs for GPA cases were 5.3-times higher than matched controls (95% CI: 4.6-6.1). 

Amongst GPA cases, age (p < 0.001), comorbidity score (p < 0.001), and being in the lowest SES group (vs. the highest, p < 0.001) were significantly associated with higher costs.  This was driven mainly by hospitalizations for GPA (see Table).  Predicted mean costs for lowest SES cases ($121,358/PY) were 1.9-times greater than the highest-SES.

Conclusion:

The medical costs of GPA cases over 5 years are substantial (averaging $81,603/PY more than matched controls from the general population), with lower SES a predictor of higher costs. 

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/low-socioeconomic-status-as-a-predictor-of-long-term-direct-medical-costs-following-diagnosis-of-granulomatosus-with-polyangiitis-a-general-population-based-cohort-study/