title: Agreement in assessment of infliximab and adalimumab levels in rheumatoid arthritis: interlaboratory and interassay comparison.
abstract: OBJECTIVE
  Infliximab (IFX) and adalimumab (ADL) drug levels and anti-drug antibodies (ADA) are assessed using a variety of techniques, therefore, results cannot accurately be compared for clinical purposes. The aim of this study was to test two infliximab (IFX) and adalimumab (ADL) ELISA versions, for drug levels and ADA, to see whether they yield similar results.
  
  
  METHODS
  ELISA versions [Promonitor® IFX R1 and R2 (V.1), Promonitor® IFX and Anti-IFX (V.2); Promonitor® ADL R1 and R2 (V.1), Promonitor® ADL and Anti-ADL (V.2) kits (Progenika Biopharma, Spain)] were used to measure drug levels and ADA in IFX (n=24) and ADL (n=24) rheumatoid arthritis-treated patients in three independent laboratories. Quantitative and qualitative agreements were evaluated using intraclass correlation coefficients (ICC), and Cohen's Kappa (κ) respectively. The Bland-Altman plots assessed differences between V.1 and V.2.
  
  
  RESULTS
  Interlaboratory agreement (ICC/κ) with V.1 was poor for IFX (0.66/0.62) and ADL (0.69/0.52) drug levels; meanwhile, high agreement was found with V.2 for IFX (0.98/0.95) and ADL (0.094/1.00). Comparison between V.1 and V.2 in each laboratory resulted in systematically higher values in V.2 than in V.1 and poor agreement (ICC/κ ranges) for IFX (0.12-0.7/ 0.19-0.42) and ADL (0.69-0.89 /0.50-0.73).
  
  
  CONCLUSIONS
  Qualitative measurements result in better agreement, as evidenced in our study. Greater agreement in V.2 compared with V.1 for IFX and ADL levels could be due to a better tune up. Further studies are required to standardise methods to establish therapeutic reference ranges.
authors: Department of Rheumatology, Hospital General Universitario Gregorio Marañón, Madrid, Spain.
authors: Lara
authors: L
authors: Valor
authors: Department of Rheumatology, Hospital General Universitario Gregorio Marañón, Madrid, Spain.
authors: Diana
authors: D
authors: Hernández-Flórez
authors: Department of Rheumatology, Hospital General Universitario Gregorio Marañón, Madrid, Spain.
authors: Inmaculada
authors: I
authors: de la Torre
authors: Laboratory Department, Hospital Marina Baixa, Villajoyosa, Alicante, Spain.
authors: Francisca
authors: F
authors: Llinares
authors: Department of Rheumatology, Hospital Marina Baixa, Villajoyosa, Alicante, Spain.
authors: José
authors: J
authors: Rosas
authors: Department of Immunology, Hospital Clinic, Barcelona, Spain.
authors: Jordi
authors: J
authors: Yagüe
authors: Department of Social Psychology and Methodology, Autonoma University, Madrid, Spain.
authors: Jesús
authors: J
authors: Garrido
authors: Department of Rheumatology, Hospital General Universitario Gregorio Marañón, Madrid, Spain.
authors: Esperanza
authors: E
authors: Naredo
mesh_terms: D000068879:Adalimumab / Q000097:blood* / Q000276:immunology; D000906:Antibodies / Q000097:blood; D018501:Antirheumatic Agents / Q000097:blood* / Q000276:immunology; D001172:Arthritis, Rheumatoid / Q000097:blood* / Q000175:diagnosis / Q000188:drug therapy / Q000276:immunology; D003430:Cross-Sectional Studies; D016903:Drug Monitoring / Q000592:standards*; D004797:Enzyme-Linked Immunosorbent Assay / Q000592:standards*; D006801:Humans; D000069285:Infliximab / Q000097:blood* / Q000276:immunology; D059021:Laboratory Proficiency Testing / Q000592:standards*; D015588:Observer Variation; D011237:Predictive Value of Tests; D019984:Quality Indicators, Health Care / Q000592:standards; D015203:Reproducibility of Results; D013030:Spain; D016896:Treatment Outcome
chemical_list: D000906:Antibodies; D018501:Antirheumatic Agents; D000069285:Infliximab; D000068879:Adalimumab