title: Determining the Minimally Important Difference in the Clinical Disease Activity Index for Improvement and Worsening in Early Rheumatoid Arthritis Patients.
abstract: OBJECTIVE
  Simplified measures to quantify rheumatoid arthritis (RA) disease activity are increasingly used. The minimum clinically important differences (MCID) for some measures, such as the Clinical Disease Activity Index (CDAI), have not been well-defined in real-world clinic settings, especially for early RA patients with low/moderate disease activity.
  
  
  METHODS
  Data from Canadian Early Arthritis Cohort patients were used to examine absolute change in CDAI in the first year after enrollment, stratified by disease activity. MCID cut points were derived to optimize the sum of sensitivity and specificity versus the gold standard of patient self-reported improvement or worsening. Sensitivity, specificity, positive predictive values, and negative predictive values were calculated against patient self-reported improvement (gold standard) and for change in pain, Health Assessment Questionnaire (HAQ), and Disease Activity Score in 28 joints (DAS28) improvement. Discrimination was examined using the area under receiver operator curves. Similar methods were used to evaluate MCIDs for worsening for patients who achieved low disease activity.
  
  
  RESULTS
  A total of 578 patients (mean ± SD age 54.1 ± 15.3 years, 75% women, median [interquartile range] disease duration 5.3 [3.3, 8.0] months) contributed 1,169 visit pairs to the improvement analysis. The MCID cut points for improvement were 12 (patients starting in high disease activity: CDAI >22), 6 (moderate: CDAI 10-22), and 1 (low disease activity: CDAI <10). Performance characteristics were acceptable using these cut points for pain, HAQ, and DAS28. The MCID for CDAI worsening among patients who achieved low disease activity was 2 units.
  
  
  CONCLUSIONS
  These minimum important absolute differences in CDAI can be used to evaluate improvement and worsening and increase the utility of CDAI in clinical practice.
authors.affiliation: University of Alabama at Birmingham.
authors.forename: J R
authors.initials: JR
authors.lastname: Curtis
authors.affiliation: University of Alabama at Birmingham.
authors.forename: S
authors.initials: S
authors.lastname: Yang
authors.affiliation: University of Alabama at Birmingham.
authors.forename: L
authors.initials: L
authors.lastname: Chen
authors.affiliation: St. Joseph's Health Center and Western University, London, Ontario, Canada.
authors.forename: J E
authors.initials: JE
authors.lastname: Pope
authors.affiliation: Mount Sinai Hospital/University of Toronto, Toronto, Ontario, Canada.
authors.forename: E C
authors.initials: EC
authors.lastname: Keystone
authors.affiliation: Centre Hospitalier de l'Université de Montreal, Montreal, Quebec, Canada.
authors.forename: B
authors.initials: B
authors.lastname: Haraoui
authors.affiliation: Centre Hospitalier Universitaire de Sherbrooke and Université de Sherbrooke, Sherbrooke, Quebec, Canada.
authors.forename: G
authors.initials: G
authors.lastname: Boire
authors.affiliation: Southlake Regional Health Centre, Newmarket, Ontario, Canada.
authors.forename: J C
authors.initials: JC
authors.lastname: Thorne
authors.affiliation: Southlake Regional Health Centre, Newmarket, Ontario, Canada.
authors.forename: D
authors.initials: D
authors.lastname: Tin
authors.affiliation: University of Manitoba, Winnipeg, Manitoba, Canada.
authors.forename: C A
authors.initials: CA
authors.lastname: Hitchon
authors.affiliation: Johns Hopkins University, Baltimore, Maryland.
authors.forename: C O
authors.initials: CO
authors.lastname: Bingham
authors.affiliation: Centre Hospitalier de l'Université de Montreal, Montreal, Quebec, Canada, and Hospital for Special Surgery, New York, New York.
authors.forename: V P
authors.initials: VP
authors.lastname: Bykerk
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D018501:Antirheumatic Agents / Q000627:therapeutic use*; D001172:Arthritis, Rheumatoid / Q000188:drug therapy* / Q000453:epidemiology / Q000503:physiopathology*; D002170:Canada; D015331:Cohort Studies; D016208:Databases, Factual; D004185:Disability Evaluation; D018450:Disease Progression; D042241:Early Diagnosis; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010147:Pain Measurement; D010808:Physical Examination / Q000379:methods; D011379:Prognosis; D012372:ROC Curve; D016059:Range of Motion, Articular / Q000502:physiology*; D015203:Reproducibility of Results; D012189:Retrospective Studies; D057566:Self Report; D012680:Sensitivity and Specificity; D012720:Severity of Illness Index; D012737:Sex Factors; D018434:Sickness Impact Profile; D016896:Treatment Outcome
chemical_list: D018501:Antirheumatic Agents