title: Disease activity measurement of rheumatoid arthritis: Comparison of the simplified disease activity index (SDAI) and the disease activity score including 28 joints (DAS28) in daily routine.
abstract: OBJECTIVE
  To assess the reliability and congruency of the Simplified Disease Activity Index (SDAI) compared with the Disease Activity Score including 28 joints (DAS28) in daily practice.
  
  
  METHODS
  In 399 consecutive rheumatoid arthritis patients (307 women, 92 men), the SDAI and the DAS28 were calculated. Additionally, 115 of them were observed for 1 year and changes of both values were recorded. Joint assessments were performed by 4 experienced physicians. DAS28 and SDAI values and the respective changes were compared by correlation and regression analyses. Reliability assessment and factor analyses were performed. Disease activity categorizing was compared by the Wilcoxon's rank sum test.
  
  
  RESULTS
  The median +/- SD scores were 3.42 +/- 1.45 for the DAS28 and 11.50 +/- 11.50 for the SDAI. Spearman's rho was 0.897 (P < 0.0001). Score changes were also significantly correlated. Reliability testing and factor analysis revealed that both scores can be regarded as monocomponent. Categorizing patients according to the European League Against Rheumatism response criteria (EULARC) or the SDAI revealed statistically significant differences between the 2 scales (P < 0.0001).
  
  
  CONCLUSIONS
  SDAI values are considerably shifted to the left compared with DAS28 levels. Internal consistency and reliability of both scores are comparable. For the differences in disease activity categorizing due to the SDAI compared with the EULARC, a major limitation of the application of this newly developed disease activity score is given, unless these incongruencies can be cleared.
authors.affiliation: Humanisklinikum Lower Austria, Lower Austrian Center for Rheumatology, Stockerau, Austria. leeb.khstockerau@aon.at
authors.forename: Burkhard F
authors.initials: BF
authors.lastname: Leeb
authors.forename: Ingrid
authors.initials: I
authors.lastname: Andel
authors.forename: Judith
authors.initials: J
authors.lastname: Sautner
authors.forename: Mirela
authors.initials: M
authors.lastname: Bogdan
authors.forename: Adil
authors.initials: A
authors.lastname: Maktari
authors.forename: Thomas
authors.initials: T
authors.lastname: Nothnagl
authors.forename: Bernhard
authors.initials: B
authors.lastname: Rintelen
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001172:Arthritis, Rheumatoid / Q000175:diagnosis* / Q000453:epidemiology* / Q000503:physiopathology; D015331:Cohort Studies; D003430:Cross-Sectional Studies; D004185:Disability Evaluation; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results; D012720:Severity of Illness Index