title: Automated alarm to detect antigen excess in serum free immunoglobulin light chain kappa and lambda assays.
abstract: BACKGROUND
  Antigen excess causing a falsely low concentration result may occur when measuring serum free immunoglobulin light chains (SFLC). Automated antigen excess detection methods are available only with some analyzers. We have now developed and verified such a method.
  
  
  METHODS
  Residuals of sera with known SFLC-κ and -λ concentrations were analyzed using Binding Site reagents and methods adapted to the Roche Cobas® c.501 analyzer.
  
  
  RESULTS
  We analyzed 117 sera for SFLC-κ and -λ and examined how the absorbance increased with time during the 7 minutes of reaction (absorbance reading points 12-70). From this an antigen excess alarm factor (ratio of absorbance increases between reading points 68-60 and 20-12, multiplied by 100) was defined. Upon our request, Roche added to our two SFLC assays a program which calculated this antigen excess alarm factor and triggered an alarm when the factor was below a defined value. We verified this antigen excess alarm function by analyzing serum from 325 persons of whom 143 were multiple myeloma patients. All samples with a known concentration above 30 mg/L triggered either an antigen excess alarm, an 'above test' alarm or both. Also, all samples above 200 mg/L (SFLC-λ) and 300 mg/L (SFLC-κ) triggered the antigen excess alarm and all but one triggered the above test alarm.
  
  
  CONCLUSIONS
  The antigen excess alarm function presented here detected all known antigen excess samples at no increased time of analysis, a reduced workload and reduced reagent cost.
authors.affiliation: Department of Medical Biochemistry, Oslo University Hospital , Ullevål , Norway.
authors.forename: Petter
authors.initials: P
authors.lastname: Urdal
authors.forename: Erik K
authors.initials: EK
authors.lastname: Amundsen
authors.forename: Karin
authors.initials: K
authors.lastname: Toska
authors.forename: Olav
authors.initials: O
authors.lastname: Klingenberg
mesh_terms: D000941:Antigens / Q000097:blood*; D001774:Blood Chemical Analysis / Q000379:methods*; D006801:Humans; D007145:Immunoglobulin kappa-Chains / Q000097:blood*; D007146:Immunoglobulin lambda-Chains / Q000097:blood*; D012680:Sensitivity and Specificity
chemical_list: D000941:Antigens; D007145:Immunoglobulin kappa-Chains; D007146:Immunoglobulin lambda-Chains
keywords: Multiple myeloma; antigen excess; free light chains; nephelometry; turbidimetry