title: An external validation study reporting poor correlation between the claims-based index for rheumatoid arthritis severity and the disease activity score.
abstract: BACKGROUND
  We conducted an external validation study to examine the correlation of a previously published claims-based index for rheumatoid arthritis severity (CIRAS) with disease activity score in 28 joints calculated by using C-reactive protein (DAS28-CRP) and the multi-dimensional health assessment questionnaire (MD-HAQ) physical function score.
  
  
  METHODS
  Patients enrolled in the Brigham and Women's Hospital Rheumatoid Arthritis Sequential Study (BRASS) and Medicare were identified and their data from these two sources were linked. For each patient, DAS28-CRP measurement and MD-HAQ physical function scores were extracted from BRASS, and CIRAS was calculated from Medicare claims for the period of 365 days prior to the DAS28-CRP measurement. Pearson correlation coefficient between CIRAS and DAS28-CRP as well as MD-HAQ physical function scores were calculated. Furthermore, we considered several additional pharmacy and medical claims-derived variables as predictors for DAS28-CRP in a multivariable linear regression model in order to assess improvement in the performance of the original CIRAS algorithm.
  
  
  RESULTS
  In total, 315 patients with enrollment in both BRASS and Medicare were included in this study. The majority (81%) of the cohort was female, and the mean age was 70 years. The correlation between CIRAS and DAS28-CRP was low (Pearson correlation coefficient = 0.07, P = 0.24). The correlation between the calculated CIRAS and MD-HAQ physical function scores was also found to be low (Pearson correlation coefficient = 0.08, P = 0.17). The linear regression model containing additional claims-derived variables yielded model R(2) of 0.23, suggesting limited ability of this model to explain variation in DAS28-CRP.
  
  
  CONCLUSIONS
  In a cohort of Medicare-enrolled patients with established RA, CIRAS showed low correlation with DAS28-CRP as well as MD-HAQ physical function scores. Claims-based algorithms for disease activity should be rigorously tested in distinct populations in order to establish their generalizability before widespread adoption.
authors.affiliation: Division of Pharmacoepidemiology and Pharmacoeconomics, Department of Medicine, Brigham and Women's Hospital & Harvard Medical School, 1620 Tremont Street, Boston, 02120, MA, USA. rdesai2@partners.org.
authors.forename: Rishi J
authors.initials: RJ
authors.lastname: Desai
authors.affiliation: Division of Pharmacoepidemiology and Pharmacoeconomics, Department of Medicine, Brigham and Women's Hospital & Harvard Medical School, 1620 Tremont Street, Boston, 02120, MA, USA. dsolomon@partners.org.|Division of Rheumatology, Immunology and Allergy, Brigham and Women's Hospital, 75 Francis Street, Boston, 02125, MA, USA. dsolomon@partners.org.
authors.forename: Daniel H
authors.initials: DH
authors.lastname: Solomon
authors.affiliation: Division of Rheumatology, Immunology and Allergy, Brigham and Women's Hospital, 75 Francis Street, Boston, 02125, MA, USA. mweinblatt@partners.org.
authors.forename: Michael E
authors.initials: ME
authors.lastname: Weinblatt
authors.affiliation: Division of Rheumatology, Immunology and Allergy, Brigham and Women's Hospital, 75 Francis Street, Boston, 02125, MA, USA. nshadick@partners.org.
authors.forename: Nancy
authors.initials: N
authors.lastname: Shadick
authors.affiliation: Division of Pharmacoepidemiology and Pharmacoeconomics, Department of Medicine, Brigham and Women's Hospital & Harvard Medical School, 1620 Tremont Street, Boston, 02120, MA, USA. skim62@partners.org.|Division of Rheumatology, Immunology and Allergy, Brigham and Women's Hospital, 75 Francis Street, Boston, 02125, MA, USA. skim62@partners.org.
authors.forename: Seoyoung C
authors.initials: SC
authors.lastname: Kim
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001172:Arthritis, Rheumatoid / Q000175:diagnosis* / Q000453:epidemiology*; D015331:Cohort Studies; D005260:Female; D006801:Humans; D008297:Male; D006278:Medicare / Q000592:standards*; D011446:Prospective Studies; D012042:Registries / Q000592:standards; D012720:Severity of Illness Index; D014481:United States / Q000453:epidemiology