title: Calprotectin in rheumatoid arthritis : association with disease activity in a cross-sectional and a longitudinal cohort.
abstract: BACKGROUND
  Calprotectin is potentially a more sensitive biomarker of disease activity in rheumatoid arthritis (RA) than conventional acute-phase proteins such as the erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) because it directly reflects inflammation in the synovium and synovial fluid rather than systemic inflammatory activity.
  
  
  OBJECTIVE
  The aim of this study was to evaluate relationships between serum calprotectin levels, disease activity, and response to treatment. Calprotectin was also investigated as a predictive marker of clinical response.
  
  
  METHODS
  This observational study included selected cohorts of patients with RA treated at La Paz University Hospital, Madrid, Spain. Associations between serum calprotectin levels and clinical and laboratory parameters were analyzed in a cross-sectional cohort of 60 patients with varying disease activity, and changes in calprotectin levels in response to treatment with infliximab were analyzed at baseline and after 3 and 6 months of treatment in a longitudinal cohort of 20 patients with very active disease.
  
  
  RESULTS
  In the cross-sectional cohort, calprotectin levels correlated with rheumatoid factor levels (r = 0.25; p < 0.05) but not with titers of antibodies to cyclic citrullinated peptide. Significant correlations were also observed between calprotectin levels and the 28 swollen joint count (28-SJC), Disease Activity Score based on a 28-joint count (DAS28), Simplified Disease Activity Index (SDAI), ESR, and CRP levels. In the longitudinal cohort, calprotectin levels at baseline were not predictive of response to treatment but significantly decreased during treatment in responders (p < 0.0001).
  
  
  CONCLUSIONS
  Calprotectin levels strongly correlate with clinical and laboratory assessments of joint inflammation and also decrease in response to treatment, indicating that calprotectin is a promising marker for assessment and monitoring of disease activity in patients with RA. Investigations are required to further evaluate its diagnostic, prognostic, and therapeutic potential.
authors: Rheumatology Unit, La Paz University Hospital, Paseo de la Castellana, 261, 28046, Madrid, Spain. miponfe@hotmail.com
authors: Miriam
authors: M
authors: García-Arias
authors: Dora
authors: D
authors: Pascual-Salcedo
authors: Susana
authors: S
authors: Ramiro
authors: Marie-Eve
authors: ME
authors: Ueberschlag
authors: Thomas M
authors: TM
authors: Jermann
authors: Carlos
authors: C
authors: Cara
authors: Emilio
authors: E
authors: Martín-Mola
authors: Alejandro
authors: A
authors: Balsa
mesh_terms: D000209:Acute-Phase Proteins / Q000378:metabolism; D000328:Adult; D000368:Aged; D000911:Antibodies, Monoclonal / Q000627:therapeutic use; D001172:Arthritis, Rheumatoid / Q000097:blood* / Q000175:diagnosis*; D015415:Biomarkers / Q000097:blood; D001799:Blood Sedimentation; D002097:C-Reactive Protein / Q000378:metabolism; D003430:Cross-Sectional Studies; D023381:Endpoint Determination; D005260:Female; D006801:Humans; D000069285:Infliximab; D039841:Leukocyte L1 Antigen Complex / Q000097:blood*; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D010456:Peptides, Cyclic / Q000378:metabolism; D011379:Prognosis; D013030:Spain; D013582:Synovial Fluid / Q000378:metabolism; D013583:Synovial Membrane / Q000378:metabolism
chemical_list: D000209:Acute-Phase Proteins; D000911:Antibodies, Monoclonal; D015415:Biomarkers; D039841:Leukocyte L1 Antigen Complex; D010456:Peptides, Cyclic; C487763:cyclic citrullinated peptide; D002097:C-Reactive Protein; D000069285:Infliximab