title: Analytical interference by monoclonal immunoglobulins on the direct bilirubin AU Beckman Coulter assay: the benefit of unsuspected diagnosis from spurious results.
abstract: BACKGROUND
  Monoclonal (M) components can interfere with the direct bilirubin (D-Bil) assay on the AU Beckman Coulter instrumentation and produce spurious results, such as D-Bil values greater than total bilirubin (T-Bil) or very low/negative D-Bil values. If properly detected, this interference may uncover undiagnosed patients with monoclonal gammopathy (MG).
  
  
  METHODS
  We investigated the interference rate on the D-Bil AU assay in serum samples known to contain M proteins along with their isotype and described the protocol set up in our laboratory to help with the diagnosis of MG based on D-Bil spurious results as first indication.
  
  
  RESULTS
  During a period of 4 years, 15.4% (345 of 2235) of serum samples containing M immunoglobulins produced erroneous D-Bil results, although no clear relationship between the magnitude or isotype of the M component and interference could be found. In total 22 new patients were diagnosed with MG based on the analytical artefact with the D-Bil as first indication.
  
  
  CONCLUSIONS
  The D-Bil interference from MG on the Beckman AU analysers needs to be made known to laboratories in order to prevent clinical confusion and/or additional workup to explain the origin of anomalous results. Although this information may not add to the management of existing patients with serum paraproteins, it can benefit patients that have not been diagnosed with MG by triggering follow up testing to determine if M components are present.
authors.forename: Elena
authors.initials: E
authors.lastname: García-González
authors.forename: Ricardo
authors.initials: R
authors.lastname: González-Tarancón
authors.forename: Maite
authors.initials: M
authors.lastname: Aramendía
authors.forename: Luis
authors.initials: L
authors.lastname: Rello
mesh_terms: D000911:Antibodies, Monoclonal / Q000097:blood*; D016477:Artifacts; D001663:Bilirubin / Q000097:blood*; D006801:Humans; D007118:Immunoassay; D007136:Immunoglobulins / Q000097:blood*; D010265:Paraproteinemias / Q000097:blood* / Q000175:diagnosis*
chemical_list: D000911:Antibodies, Monoclonal; D007136:Immunoglobulins; D001663:Bilirubin