Objectives To develop a claims-based severity index for rheumatoid arthritis (RA) using large U.S. claims data.

Methods Adult patients with at least two RA diagnoses 2 months apart were identified from a large U.S. claims database (10/1/2008-09/30/2009). Patients were required to have at least 12 months continuous health plan enrollment before and after the index date (first RA diagnosis date). A severity index for rheumatoid arthritis (SIFRA) was developed by calculating a weighted sum of 47 RA-related indicators including laboratory, clinical and functional status, extra-articular manifestations, surgical history, and medications assessed by an expert Delphi panel of six rheumatologists. Two versions of SIFRA were derived for patients with and without laboratory information. Correlations between SIFRA and previously validated claims-based indexes for RA severity (CIRAS), and other traditional comorbidity indexes were calculated. The relationship between SIFRA and heath care costs was also examined using histograms.

Results The Spearman’s rank correlations between SIFRA and CIRAS were 0.525 for SIFRA without laboratory data and 0.539 for SIFRA with laboratory data. The correlations between SIFRA and the Charlson Comorbidity Index (0.1503 without, 0.1135 with laboratory data), Elixhauser Index (0.105 without, 0.079 with laboratory data) and Chronic Disease Score (CDS) (0.255 without, 0.239 with laboratory data) were low. Histograms showed that patients in the upper tercile of SIFRA incurred $9,123 more all-cause health care costs and $1,326 more RA-related health care costs than patients in the lower tercile of SIFRA.

Conclusions SIFRA demonstrated evidence of being a significant determinant of total and RA-related health care costs for RA patients, and was found to have moderate correlations with the previously validated CIRAS score, and. To control for severity in RA-related outcomes research, this study suggests that SIFRA could be an important methodological tool.

Disclosure of Interest None Declared