Mortality trends in rheumatoid arthritis: the role of rheumatoid factor

OBJECTIVE: We previously demonstrated a widening in the mortality gap between subjects with rheumatoid arthritis (RA) and the general population. We examined the contribution of rheumatoid factor (RF) positivity on overall mortality trends and cause-specific mortality. METHODS: A population-based RA incidence cohort (1955-1995, and aged >or= 18 yrs) was followed longitudinally until death or January 1, 2006. The underlying cause of death as coded from national mortality statistics and grouped according to ICD-9/10 chapters was used to define cause-specific mortality. Expected cause-specific mortality rates were estimated by applying the age-, sex-, and calendar-year-specific mortality rates from the general population to the RA cohort. Poisson regression was used to model the observed overall and cause-specific mortality rates according to RF status, accounting for age, sex, disease duration, and calendar year. RESULTS: A cohort of 603 subjects (73% female; mean age 58 yrs) with RA was followed for a mean of 16 years, during which 398 died. Estimated survival at 30 years after RA incidence was 26.0% in RF+ RA subjects compared to 36.0% expected (p < 0.001), while in RF- RA subjects, estimated survival was 29.1% compared to 28.3% expected (p = 0.9). The difference between the observed and the expected mortality in the RF+ RA subjects increased over time, resulting in a widening of the mortality gap, while among RF- RA subjects, observed mortality was very similar to the expected mortality over the entire time period. Among RF+ RA subjects, cause-specific mortality was higher than expected for cardiovascular relative risk (RR) 1.50; 95% confidence interval (CI) 1.22, 1.83] and respiratory diseases RR 3.49; 95% CI 2.51, 4.72]. Among RF- RA subjects, no significant differences were found between observed and expected cause-specific mortality. CONCLUSION: The widening in the mortality gap between RA subjects and the general population is confined to RF+ RA subjects and largely driven by cardiovascular and respiratory deaths.