title: Differential response of serum amyloid A to different therapies in early rheumatoid arthritis and its potential value as a disease activity biomarker.
abstract: The aim was to compare the effect of etanercept (ETN) and conventional synthetic disease-modifying anti-rheumatic drug (DMARD) therapy on serum amyloid A (SAA) levels and to determine whether SAA reflects rheumatoid arthritis (RA) disease activity better than C-reactive protein (CRP).
  
  
  
  We measured SAA and CRP at baseline, 24, 48, and 102 week follow-up visits in 594 patients participating in the Treatment of early RA (TEAR) study. We used Spearman correlation coefficients (rho) to evaluate the relationship between SAA and CRP and mixed effects models to determine whether ETN and methotrexate (MTX) treatment compared to triple DMARD therapy differentially lowered SAA. Akaike information criteria (AIC) were used to determine model fits.
  
  
  
  SAA levels were only moderately correlated with CRP levels (rho = 0.58, p < 0.0001). There were significant differences in SAA by both visit (p = 0.0197) and treatment arm (p = 0.0130). RA patients treated with ETN plus MTX had a larger reduction in SAA than patients treated with traditional DMARD therapy. Similar results were found for serum CRP by visit (p = 0.0254) and by treatment (p < 0.0001), with a more pronounced difference than for SAA. Across all patients and time points, models of the disease activity score of 28 joints (DAS28)-erythrocyte sedimentation rate (ESR) using SAA levels were better than models using CRP; the ΔAIC between the SAA and CRP models was 305.
  
  
  
  SAA may be a better biomarker of RA disease activity than CRP, especially during treatment with tumor necrosis factor (TNF) antagonists. This warrants additional studies in other cohorts of patients on treatment for RA.
  
  
  
  (ClinicalTrials.gov identifier: NCT00259610 , Date of registration: 28 November 2005).
authors.affiliation: Department of Medicine, Division of Rheumatology and Clinical Immunology, University of Pittsburgh, 3500 Terrace Street, Pittsburgh, PA, 15261, USA. hwangyg@upmc.edu.
authors.forename: Yong Gil
authors.initials: YG
authors.lastname: Hwang
authors.affiliation: Department of Epidemiology, School of Public Health, University of Pittsburgh, 130 DeSoto Street, 127 Parran Hall, Pittsburgh, PA, 15261, USA.
authors.forename: Goundappa K
authors.initials: GK
authors.lastname: Balasubramani
authors.affiliation: Department of Medicine, Division of Rheumatology and Clinical Immunology, University of Pittsburgh, 3500 Terrace Street, Pittsburgh, PA, 15261, USA.
authors.forename: Ilinca D
authors.initials: ID
authors.lastname: Metes
authors.affiliation: Department of Medicine, Division of Rheumatology and Clinical Immunology, University of Pittsburgh, 3500 Terrace Street, Pittsburgh, PA, 15261, USA.|AbbVie Inc, 100 Research Dr, Worcester, MA, 01605, USA.
authors.forename: Marc C
authors.initials: MC
authors.lastname: Levesque
authors.affiliation: Department of Medicine, Division of Clinical Immunology and Rheumatology Birmingham, University of Alabama at Birmingham, Shelby Building, Room 178B, 1825 University Blvd., Birmingham, AL, 35294-2182, USA.
authors.forename: S Louis
authors.initials: SL
authors.lastname: Bridges
authors.affiliation: Department of Medicine, Division of Rheumatology and Clinical Immunology, University of Pittsburgh, 3500 Terrace Street, Pittsburgh, PA, 15261, USA.
authors.forename: Larry W
authors.initials: LW
authors.lastname: Moreland
mesh_terms: D000328:Adult; D018501:Antirheumatic Agents / Q000627:therapeutic use*; D001172:Arthritis, Rheumatoid / Q000097:blood* / Q000188:drug therapy*; D015415:Biomarkers / Q000097:blood*; D002097:C-Reactive Protein / Q000032:analysis; D004311:Double-Blind Method; D000068800:Etanercept / Q000627:therapeutic use; D005260:Female; D006801:Humans; D007118:Immunoassay; D008297:Male; D008727:Methotrexate / Q000627:therapeutic use; D008875:Middle Aged; D000685:Serum Amyloid A Protein / Q000032:analysis*
chemical_list: D018501:Antirheumatic Agents; D015415:Biomarkers; D000685:Serum Amyloid A Protein; D002097:C-Reactive Protein; D000068800:Etanercept; D008727:Methotrexate
keywords: C-reactive protein; Early rheumatoid arthritis; Etanercept; Serum amyloid A