Background/Purpose: Treat to target guidelines recommend
achieving a state of remission or low disease activity for rheumatoid arthritis
(RA) patients. However, the benefit of lower disease activity for reduction of
adverse events and costs is not clear. Our objective was to evaluate clinical
outcomes and economic costs associated with RA disease activity states.

Methods: We used CORRONA data linked to national Medicare
data to identify RA patients and their disease activity, measured using the
Clinical Disease Activity Index (CDAI) captured at each registry visit. CDAI
was modeled using a time-varying, area under the curve approach. Follow-up
began at the date of the 2nd registry visit and the analysis was censored at
time of the first event, 12/31/2012. Outcomes included all cause
hospitalization, a composite of hospitalization or ED visits, mortality, and
paid monthly healthcare costs. Outcome-specific Cox proportional hazards models
evaluated the adjusted hazard ratios (aHR) between disease activity and
outcomes, controlling for potential confounders. Costs were analyzed with mixed
models using a Gaussian distribution with log transformation.

Results: Slightly depending on outcome, 4593 RA patients
contributed up to 14,756 person years. Mean (SD) age was 69.8 (9.3) years, 75%
women. At baseline, 59% of patients were in remission or low disease activity
(LDA); 43.8% were on biologics. There was a strong dose-response relationship
between the four categories of RA disease activity (remission, low, moderate,
high) and incidence rate for hospitalization (13.7, 19.0, 23.1, 29.9 per
100py). For hospitalization, all aHR were significant: 0.65 (remission), 0.81
(low), and 1.16 (high) referent to moderate. Similar crude and adjusted trends
were observed for other outcomes. The crude difference in monthly costs between
remission ($956/mo) and moderate disease activity ($1607/mo) was $651; the
adjusted difference was -441.60 (-563.96, -319.24) per month.

Conclusion: Lower disease activity states in RA were
associated with incrementally reduced risks of all-cause hospitalization, ED
visits, mortality, and healthcare costs in a dose-dependent fashion.

Table 2a: Crude Rates* of Outcomes, by RA Disease Activity
Associated with Cumulative, Time-Averaged CDAI

*Rate per 100py