title: A Proposed Serum Calprotectin IgG Cut-Off Level for Diagnosing Inflammatory Arthritis.
abstract: BACKGROUND
  The identification and validation of soluble markers provide significant opportunities for managing patients with rheumatic diseases, and calprotectin may be an alternative laboratory biomarker of inflammatory rheumatoid arthritis (RA) and psoriatic arthritis (PsA) even though its levels may vary considerably. The aim of this study was to propose a calprotectin cut-off value that would be useful for distinguishing patients with inflammatory arthritis or noninflammatory arthritis (NIA) in clinical practice.
  
  
  METHODS
  A commercial enzyme-linked immunosorbent assay was used to measure serum calprotectin levels in patients with RA, ankylosing spondylitis (AS), PsA and controls with NIA. All of the patients had been treated with biological disease-modifying anti-rheumatic drugs (DMARDs) for about 12 months after previous failure on conventional DMARDs.
  
  
  RESULTS
  Receiver operating characteristic (ROC) analysis showed that serum calprotectin levels significantly differentiated the samples of the patients with inflammatory rheumatic disease from those of the controls. A serum calprotectin level of > 0.9 μg/mL (the optimal predictive cut-off value in the ROC analysis) had a sensitivity of 95.3%, a specificity of 82.2%, a positive likelihood ratio (LR) of 5.35 and a negative LR of 0.057.
  
  
  CONCLUSIONS
  Our findings suggest that serum calprotectin levels are useful in clinical practice to distinguish patients with inflammatory arthritis and NIA. Further studies of a larger population are suggested.
authors.affiliation: Immunology and Allergology Laboratory Unit, San Giovanni di Dio Hospital, Via Torregalli 3, 50143 Florence, Italy.
authors.forename: Valentina
authors.initials: V
authors.lastname: Grossi
authors.affiliation: Immunology and Allergology Laboratory Unit, S. Giovanni di Dio Hospital, Florence, Italy.
authors.forename: Maria
authors.initials: M
authors.lastname: Infantino
authors.affiliation: Immunology and Allergology Laboratory Unit, S. Giovanni di Dio Hospital, Florence, Italy.
authors.forename: Mariangela
authors.initials: M
authors.lastname: Manfredi
authors.affiliation: Immunology and Allergology Laboratory Unit, S. Giovanni di Dio Hospital, Florence, Italy.
authors.forename: Francesca
authors.initials: F
authors.lastname: Meacci
authors.affiliation: Rheumatology Unit, S. Giovanni di Dio Hospital, Florence, Italy.
authors.forename: Emanuele
authors.initials: E
authors.lastname: Bellio
authors.affiliation: Rheumatology Unit, S. Giovanni di Dio Hospital, Florence, Italy.
authors.forename: Valerio
authors.initials: V
authors.lastname: Bellio
authors.affiliation: Rheumatology Unit, S. Giovanni di Dio Hospital, Florence, Italy.
authors.forename: Francesca Li
authors.initials: FL
authors.lastname: Gobbi
authors.affiliation: Eurospital SpA, Trieste, Italy.
authors.forename: Simone
authors.initials: S
authors.lastname: Ugolini
authors.affiliation: Eurospital SpA, Trieste, Italy.
authors.forename: Stefano
authors.initials: S
authors.lastname: Catani
authors.affiliation: Rheumatology Unit, L. Sacco University Hospital, Milan, Italy.
authors.forename: Piercarlo
authors.initials: P
authors.lastname: Sarzi-Puttini
authors.affiliation: IRCCS Galeazzi Orthopedic Institute, Milan, Italy.
authors.forename: Fabiola
authors.initials: F
authors.lastname: Atzeni
authors.affiliation: Rheumatology Unit, S. Giovanni di Dio Hospital, Florence, Italy.
authors.forename: Maurizio
authors.initials: M
authors.lastname: Benucci
mesh_terms: D000368:Aged; D019540:Area Under Curve; D015535:Arthritis, Psoriatic / Q000097:blood* / Q000175:diagnosis*; D001172:Arthritis, Rheumatoid / Q000097:blood* / Q000175:diagnosis*; D005260:Female; D006801:Humans; D039841:Leukocyte L1 Antigen Complex / Q000097:blood*; D008297:Male; D008875:Middle Aged; D012372:ROC Curve; D012680:Sensitivity and Specificity
chemical_list: D039841:Leukocyte L1 Antigen Complex
keywords: Calprotectin; biomarkers; disease activity; inflammatory arthritis; non inflammatory arthritis; psoriatic arthritis; rheumatoid arthritis; spondyloarthritis