title: Agreement between the DAS28-CRP assessed with 3 and 4 variables in patients with rheumatoid arthritis treated with biological agents in the daily clinic.
abstract: OBJECTIVE
  The Disease Activity Score-28-C-reactive Protein 4 [DAS28-CRP(4)] composite measure for rheumatoid arthritis (RA) is based on 4 variables: tender and swollen joint counts, CRP, and patient global assessment. DAS28-CRP(3) includes only 3 variables, because patient global assessment has been omitted. Thresholds for low and high disease activity are the same for the 2 scores. The objective of our study was to compare the 2 DAS scores and their responses on the individual patient level.
  
  
  METHODS
  Baseline and 12-week disease activity data from 239 patients with RA treated with a biological agent were extracted from the Danish registry for biological treatment (DANBIO). Cohen's effect sizes (ES) and disease activity levels according to the DAS thresholds were assessed. The Bland-Altman method was used to examine the bias between the DAS scores and the 95% limits of agreement (LoA).
  
  
  RESULTS
  Baseline values for DAS28-CRP(4) and DAS28-CRP(3) were 4.8 ± 1.2 and 4.6 ± 1.1, respectively. At 12 weeks, DAS28-CRP(4) had improved by -1.39 ± 1.34 (p < 0.0001). At that timepoint the bias of DAS28-CRP(3) was -0.07 (LoA -0.69, 0.55) (p < 0.0001). The bias of the DAS28-CRP(3) response was +0.21 (LoA -0.49, 0.91) (p < 0.0001). ES for DAS28-CRP(4) was 1.2 ± 1.1 versus 1.1 ± 1.1 for DAS28-CRP(3) (p < 0.0001). Compared to DAS28-CRP(4), DAS28-CRP(3) categorized 33% fewer patients as having a high level of disease activity, 8% fewer patients as good responders, and 12% more patients as nonresponders.
  
  
  CONCLUSIONS
  Mean values of DAS28-CRP(4) and DAS28-CRP(3) agreed well, but in the individual patient the difference between the scores and their responses may be substantial.
authors: Department of Rheumatology/Internal Medicine C, Copenhagen University Hospital Gentofte, Denmark. rintek@dadlnet.dk
authors: Ole Rintek
authors: OR
authors: Madsen
mesh_terms: D000328:Adult; D000368:Aged; D018501:Antirheumatic Agents / Q000627:therapeutic use*; D001172:Arthritis, Rheumatoid / Q000097:blood* / Q000188:drug therapy; D001688:Biological Products / Q000627:therapeutic use*; D002097:C-Reactive Protein / Q000032:analysis*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012042:Registries; D012720:Severity of Illness Index; D016896:Treatment Outcome
chemical_list: D018501:Antirheumatic Agents; D001688:Biological Products; D002097:C-Reactive Protein