title: Calprotectin more accurately discriminates the disease status of rheumatoid arthritis patients receiving tocilizumab than acute phase reactants.
abstract: OBJECTIVE
  To compare the accuracy of serum calprotectin levels, CRP and ESR in stratifying disease activity in RA patients receiving tocilizumab (TCZ).
  
  
  METHODS
  Cross-sectional study of 33 RA patients receiving TCZ. DAS28, Simplified Disease Activity Index, Clinical Disease Activity Index, joint counts and serum levels of CRP, ESR, calprotectin and TCZ were measured. Associations between calprotectin, ESR and CRP and articular indices were analysed by correlation and linear regression. The accuracy and discriminatory capacity of calprotectin was assessed by receiver operating characteristic curves (area under the curve).
  
  
  RESULTS
  Calprotectin levels, but not CRP or ESR, were strongly correlated with all composite indices (all r coefficients over 0.50). Calprotectin, but not CRP or ESR, was significantly lower in patients in remission compared with those with low disease activity [1.57 μg/ml (s.d. 1) vs 3.35 μg/ml (s.d. 1), P = 0.001]. In a fully adjusted model (R(2) = 0.82), DAS28-ESR increased 0.48 units per μg/ml calprotectin increase (P < 0.001). Using a DAS28 >3.2 as the reference variable, calprotectin showed an area under the curve of 0.922, and the best cut-off was 5.19 μg/ml (odds ratio 11.5). CRP levels, but not calprotectin, were dependent on detectable TCZ trough serum levels.
  
  
  CONCLUSIONS
  Calprotectin serum levels seem to be an accurate biomarker for assessing disease activity in RA patients receiving TCZ.
authors.affiliation: Department of Rheumatology and.
authors.forename: José
authors.initials: J
authors.lastname: Inciarte-Mundo
authors.affiliation: Department of Rheumatology and.
authors.forename: Virginia
authors.initials: V
authors.lastname: Ruiz-Esquide
authors.affiliation: Department of Rheumatology and.
authors.forename: Maria Victoria
authors.initials: MV
authors.lastname: Hernández
authors.affiliation: Department of Rheumatology and.
authors.forename: Juan D
authors.initials: JD
authors.lastname: Cañete
authors.affiliation: Department of Rheumatology and.
authors.forename: Sonia Raquel
authors.initials: SR
authors.lastname: Cabrera-Villalba
authors.affiliation: Department of Rheumatology and.
authors.forename: Julio
authors.initials: J
authors.lastname: Ramirez
authors.affiliation: Department of Immunology, Hospital Clinic, University of Barcelona, Barcelona, Spain.
authors.forename: Jordi
authors.initials: J
authors.lastname: Yagüe
authors.affiliation: Department of Rheumatology and sanmarti@clinic.cat.
authors.forename: Raimon
authors.initials: R
authors.lastname: Sanmarti
mesh_terms: D000328:Adult; D061067:Antibodies, Monoclonal, Humanized / Q000627:therapeutic use*; D018501:Antirheumatic Agents / Q000627:therapeutic use*; D001172:Arthritis, Rheumatoid / Q000097:blood / Q000188:drug therapy*; D015415:Biomarkers / Q000097:blood; D001799:Blood Sedimentation; D002097:C-Reactive Protein / Q000378:metabolism*; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D039841:Leukocyte L1 Antigen Complex / Q000097:blood*; D008297:Male; D008875:Middle Aged; D012720:Severity of Illness Index
chemical_list: D061067:Antibodies, Monoclonal, Humanized; D018501:Antirheumatic Agents; D015415:Biomarkers; D039841:Leukocyte L1 Antigen Complex; D002097:C-Reactive Protein; C502936:tocilizumab
keywords: calprotectin; disease activity; rheumatoid arthritis; tocilizumab