title: Detection of infliximab levels and anti-infliximab antibodies: a comparison of three different assays.
abstract: BACKGROUND
  Formation of antibodies to infliximab (ATI) inversely correlates with functional drug levels and clinical outcome. Comparison of drug levels and anti-drug antibody monitoring is hampered by lack of standardisation.
  
  
  OBJECTIVE
  To determine the correlation between three different assays for measuring infliximab and ATI.
  
  
  METHODS
  Serum samples and spiked controls (total 62) were evaluated in a blinded way in infliximab and ATI assays developed by Sanquin Amsterdam, Netherlands (A), Laboratory for Pharmaceutical Biology, KU Leuven, Belgium (B) and a commercially available kit from Biomedical Diagnostics (BMD), Paris, France (C) performed by the University Medical Center Groningen (UMCG), Netherlands.
  
  
  RESULTS
  All infliximab assays showed a linear quantitative correlation (Pearson r = 0.91 for A vs. B, 0.83 for A vs. C and 0.73 for B vs. C). Assay C detected infliximab in 11 samples (18%) not detected by A and B, including samples containing only ATI. All ATI assays showed a good linear correlation (Pearson r = 0.95 for A vs. B, 0.99 for A vs. C and 0.97 for B vs. C). Assay A detected ATI in five samples with low ATI that were not detected by assays B and C. Assay B did not detect ATI in three patient samples with low ATI according to assays A and C.
  
  
  CONCLUSIONS
  There is a good correlation of infliximab and antibodies to infliximab measurements between these assays. Nevertheless, the Biomedical Diagnostics kit detected false positive infliximab levels in 18% of the samples.
authors.affiliation: Laboratory for Pharmaceutical Biology, KU Leuven, Leuven, Belgium. niels.vandecasteele@pharm.kuleuven.be
authors.forename: N
authors.initials: N
authors.lastname: Vande Casteele
authors.forename: D J
authors.initials: DJ
authors.lastname: Buurman
authors.forename: M G G
authors.initials: MG
authors.lastname: Sturkenboom
authors.forename: J H
authors.initials: JH
authors.lastname: Kleibeuker
authors.forename: S
authors.initials: S
authors.lastname: Vermeire
authors.forename: T
authors.initials: T
authors.lastname: Rispens
authors.forename: D
authors.initials: D
authors.lastname: van der Kleij
authors.forename: A
authors.initials: A
authors.lastname: Gils
authors.forename: G
authors.initials: G
authors.lastname: Dijkstra
mesh_terms: D000894:Anti-Inflammatory Agents, Non-Steroidal / Q000097:blood* / Q000276:immunology; D000906:Antibodies / Q000097:blood*; D000911:Antibodies, Monoclonal / Q000097:blood* / Q000276:immunology*; D000937:Antigen-Antibody Reactions; D015415:Biomarkers / Q000097:blood; D005189:False Positive Reactions; D006801:Humans; D007118:Immunoassay / Q000379:methods*; D000069285:Infliximab; D011933:Reagent Kits, Diagnostic / Q000592:standards; D013223:Statistics as Topic
chemical_list: D000894:Anti-Inflammatory Agents, Non-Steroidal; D000906:Antibodies; D000911:Antibodies, Monoclonal; D015415:Biomarkers; D011933:Reagent Kits, Diagnostic; D000069285:Infliximab