title: Value of commonly measured laboratory tests as biomarkers of disease activity and predictors of relapse in eosinophilic granulomatosis with polyangiitis.
abstract: OBJECTIVE
  The aim of this study was to assess the clinical value of absolute eosinophil count, serum IgE, ESR and CRP as longitudinal biomarkers of disease activity and predictors of relapse in eosinophilic granulomatosis with polyangiitis (Churg-Strauss, EGPA).
  
  
  METHODS
  Patients were selected from an observational EGPA cohort. Absolute eosinophil count, IgE, ESR and CRP were measured quarterly. Disease activity was defined by validated assessment tools. The association of tests with disease activity was assessed via regression models, adjusting for repeated measures and treatment status. Survival analysis was used to determine if laboratory tests were predictive of the 3 month future flare risk.
  
  
  RESULTS
  Seventy-four per cent of 892 study visits in 141 patients occurred while patients were on treatment, mostly during remission or mild disease activity, defined as a BVAS for Wegener's granulomatosis (BVAS/WG) of 1 or 2. Correlations between absolute eosinophil count, IgE, ESR and CRP were mostly low or non-significant (r = -0.08 to 0.44). There were few weak associations with disease activity [absolute eosinophil count: OR) 1.01/100 U (95% CI 1.01, 1.02); ESR: OR 1.15/10 mg/l increase (95% CI 1.04, 1.27)]. When BVAS/WG ≥1 defined active disease, the absolute eosinophil count [hazard ratio (HR) 1.01/100 U (95% CI 1.01, 1.02)] was weakly predictive of flare. When BVAS/WG ≥3 defined active disease, ESR was weakly predictive of flare [HR 1.52/10 mm/h increase (95% CI 1.17, 1.67)].
  
  
  CONCLUSIONS
  The absolute eosinophil count, IgE, ESR and CRP have limitations as longitudinal biomarkers of disease activity or predictors of flare in EGPA. These findings suggest that novel biomarkers of disease activity for EGPA are needed.
authors.affiliation: National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS), National Institutes of Health, Bethesda, MD.
authors.forename: Peter C
authors.initials: PC
authors.lastname: Grayson
authors.affiliation: Section of Rheumatology, Boston University School of Medicine, Boston, MA, USA.
authors.forename: Paul A
authors.initials: PA
authors.lastname: Monach
authors.affiliation: Division of Rheumatology, Mount Sinai Hospital, Toronto, ON, Canada.
authors.forename: Christian
authors.initials: C
authors.lastname: Pagnoux
authors.affiliation: Department of Biostatistics, University of South Florida, Tampa, FL.
authors.forename: David
authors.initials: D
authors.lastname: Cuthbertson
authors.affiliation: Division of Rheumatology, Mount Sinai Hospital, Toronto, ON, Canada.
authors.forename: Simon
authors.initials: S
authors.lastname: Carette
authors.affiliation: Center for Vasculitis Care and Research, Cleveland Clinic, Cleveland, OH, USA.
authors.forename: Gary S
authors.initials: GS
authors.lastname: Hoffman
authors.affiliation: Division of Rheumatology, McMaster University, Hamilton, ON, Canada.
authors.forename: Nader A
authors.initials: NA
authors.lastname: Khalidi
authors.affiliation: Division of Rheumatology, University of Utah, Salt Lake City, UT.
authors.forename: Curry L
authors.initials: CL
authors.lastname: Koening
authors.affiliation: Center for Vasculitis Care and Research, Cleveland Clinic, Cleveland, OH, USA.
authors.forename: Carol A
authors.initials: CA
authors.lastname: Langford
authors.affiliation: Division of Rheumatology, University of Pittsburgh, Pittsburgh, PA.
authors.forename: Kathleen
authors.initials: K
authors.lastname: Maksimowicz-McKinnon
authors.affiliation: Division of Rheumatology, Johns Hopkins University, Baltimore, MD.
authors.forename: Philip
authors.initials: P
authors.lastname: Seo
authors.affiliation: Division of Pulmonary and Critical Care Medicine, Mayo Clinic of Medicine, Rochester.
authors.forename: Ulrich
authors.initials: U
authors.lastname: Specks
authors.affiliation: Division of Rheumatology, Mayo Clinic College of Medicine, Rochester, MN and.
authors.forename: Steven R
authors.initials: SR
authors.lastname: Ytterberg
authors.affiliation: Division of Rheumatology, University of Pennsylvania, Philadelphia, PA, USA pmerkel@upenn.edu.
authors.forename: Peter A
authors.initials: PA
authors.lastname: Merkel
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015415:Biomarkers / Q000097:blood; D001799:Blood Sedimentation; D002097:C-Reactive Protein / Q000378:metabolism; D002452:Cell Count; D015331:Cohort Studies; D003955:Diagnostic Tests, Routine / Q000379:methods*; D004802:Eosinophilia / Q000097:blood* / Q000175:diagnosis*; D004804:Eosinophils / Q000473:pathology; D005260:Female; D014890:Granulomatosis with Polyangiitis / Q000097:blood* / Q000175:diagnosis*; D006801:Humans; D007073:Immunoglobulin E / Q000097:blood; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D012008:Recurrence; D012044:Regression Analysis; D012720:Severity of Illness Index
chemical_list: D015415:Biomarkers; D007073:Immunoglobulin E; D002097:C-Reactive Protein
keywords: Churg–Strauss syndrome; biomarker; eosinophil; eosinophilic granulomatosis with polyangiitis; vasculitis