title: [A study on calculating the ankylosing spondylitis disease activity score according to the C-reactive protein level].
abstract: OBJECTIVE
  To study the prediction value of C-reactive protein (CRP) level to ankylosing spondylitis disease activity score (ASDAS), the most widely used activity score in ankylosing spondylitis (AS).
  
  
  METHODS
  A total of 386 patients with AS were enrolled and divided into 2 groups by CRP ≥ 3.5 mg/L (n=266) and CRP<3.5 mg/L(n=120). ASDAS-CRP was evaluated in patients with CRP below the normal range (3.5 mg/L) in different subgroups. Three methods were used to test the consistency between ASDAS-CRP and ASDAS-erythrocyte sedimentation rate (ESR).
  
  
  RESULTS
  The ASDAS-CRP showed a good correlation with the ASDAS-ESR when CRP level was ≥ 3.5 mg/L (r=0.899, P=0.000). In the group of CRP <3.5 mg/L, ASDAS-ESR showed better consistency with ASDAS-CRP when CRP level was below 1.5 mg/L(intra-class correlation coefficient 0.902; kappa coefficient 0.70). By the evaluation of variant gradient matrix, CRP 1.5 mg/L coincided with disease activity states.
  
  
  CONCLUSIONS
  There is good consistency between ASDAS-CRP and ASDAS-ESR. When CRP level is below the normal range, 1.5 mg/L could be a cut-off value to calculate the optimal ASDAS-CRP score.
authors.affiliation: Department of Rheumatology, Chinese PLA General Hospital, Beijing 100853, China.
authors.forename: Xiaojian
authors.initials: X
authors.lastname: Ji
authors.forename: Jun
authors.initials: J
authors.lastname: Du
authors.forename: Jian
authors.initials: J
authors.lastname: Zhu
authors.forename: Feng
authors.initials: F
authors.lastname: Huang
authors.forename: Jianglin
authors.initials: J
authors.lastname: Zhang
mesh_terms: D001799:Blood Sedimentation; D002097:C-Reactive Protein / Q000032:analysis*; D006801:Humans; D012720:Severity of Illness Index; D013167:Spondylitis, Ankylosing / Q000097:blood / Q000175:diagnosis*
chemical_list: D002097:C-Reactive Protein