Development and validation of a risk score for serious infection in patients with rheumatoid arthritis

Objective Infection risk is increased in patients with rheumatoid arthritis (RA), and accurate assessment of the risk of infection could inform clinical decision‐making. This study was undertaken to develop and validate a score to predict the 1‐year risk of serious infection in patients with RA. Methods We studied a population‐based cohort of Olmsted County, Minnesota residents with incident RA ascertained in 1955–1994 whose members were followed up longitudinally, via complete medical records, until January 2000. The validation cohort included residents with incident RA ascertained in 1995–2007. The outcome measure included all serious infections (requiring hospitalization or intravenous antibiotics). Potential predictors were examined using multivariable Cox models. The risk score was estimated directly from the multivariable model, and performance was assessed in the validation cohort using Harrell's C statistic. Results Among the 584 RA patients in the original cohort (72% female; mean age 57.5 years), who were followed up for a median of 9.9 years, 252 had ≥1 serious infection (646 total infections). Components of the risk score included age, previous serious infection, corticosteroid use, elevated erythrocyte sedimentation rate, extraarticular manifestations of RA, and comorbidities (coronary heart disease, heart failure, peripheral vascular disease, chronic lung disease, diabetes mellitus, alcoholism). Validation analysis revealed good discrimination (C statistic 0.80). Conclusion RA disease characteristics and comorbidities can be used to accurately assess the risk of serious infection in patients with RA. Knowledge of risk of serious infection in RA patients can influence clinical decision making and inform strategies to reduce and prevent the occurrence of these infections.