title: Monoclonal and polyclonal immunoglobulin interference in a conjugated bilirubin assay.
abstract: BACKGROUND
  Monoclonal proteins can interfere with the conjugated bilirubin assay on the Beckman Coulter AU5400 and AU2700 instruments and produce spurious results. Protein depletion eliminates the interference, suggesting that monoclonal proteins cause the problem.
  
  
  OBJECTIVE
  To determine the interference rate with the Beckman Coulter AU5400 and AU2700 conjugated bilirubin assay and to identify the interfering substance.
  
  
  METHODS
  Beckman Coulter bilirubin results from 33,720 samples analyzed during 6 months were evaluated for interference. On a subset of samples, protein G columns were used to specifically remove immunoglobulin G (IgG) to determine the cause of the interference. Another 117 samples containing a (known) monoclonal protein were selected to determine the interference rate.
  
  
  RESULTS
  From 26 different patients, 103 samples had conjugated bilirubin results greater than the total bilirubin for a false-positive rate of 0.3%. Removal of IgG from a subset of those samples with IgG monoclonal protein and increased polyclonal IgG eliminated the conjugated bilirubin interference. In separate, selected samples containing monoclonal proteins, the false-positive interference rate was 7.7% (9 of 117) and was greatest when the monoclonal protein concentration was greater than 4 g/dL. Another 11 of the 117 samples (9.4%) with monoclonal proteins exhibited assay interference by producing false-negative results. The overall interference rate, therefore, was 17.1%.
  
  
  CONCLUSIONS
  The false-positive interference rate for the Beckman Coulter conjugated bilirubin assay was 0.3% for routinely analyzed serum/plasma samples. In addition to monoclonal proteins, we found that polyclonal immunoglobulins can also interfere with the conjugated bilirubin assay. The overall interference rate was 17.1% for samples with a monoclonal protein.
authors: From the Department of Pathology and Laboratory Medicine, David Geffen School of Medicine at UCLA, Los Angeles, California.
authors: Lu
authors: L
authors: Song
authors: Kathleen A
authors: KA
authors: Kelly
authors: Anthony W
authors: AW
authors: Butch
mesh_terms: D000368:Aged; D001663:Bilirubin / Q000031:analogs & derivatives* / Q000097:blood; D001774:Blood Chemical Analysis / Q000379:methods*; D001797:Blood Protein Electrophoresis; D005189:False Positive Reactions; D005260:Female; D006801:Humans; D007118:Immunoassay; D007074:Immunoglobulin G / Q000097:blood; D007136:Immunoglobulins / Q000097:blood*; D008875:Middle Aged; D010266:Paraproteins / Q000032:analysis
chemical_list: D007074:Immunoglobulin G; D007136:Immunoglobulins; D010266:Paraproteins; D001663:Bilirubin