title: Effect of sample dilution on serum free light chain concentration by immunonephelometric assay.
abstract: BACKGROUND
  Free light chains (FLC) are useful biomarkers in the assessment of plasma cell disorders. Concerns have been raised about some technical aspects of the assay. This report examined the occurrence of dilution anomalies and/or antigen excess.
  
  
  METHODS
  FLC were determined on a BNII instrument at at-least two dilutions (100- and 2000-fold) in 2088 consecutive samples from 865 different patients. In part of them, the 400-fold dilution was also available.
  
  
  RESULTS
  Higher than 2-fold differences and inconsistencies ["<" or ">" result at one dilution not consistent with the result obtained at another dilution] between the 100- and 2000-fold dilutions were found in 12.7% of patients for κ FLC and in 3.1% of patients for λ FLC. More than 4-fold differences between results obtained at the 2000-fold and the 100-fold dilutions were observed in 5.4% of patients for κ FLC and in 1.2% of patients for λ FLC.
  
  
  CONCLUSIONS
  The FLC assay on BNII suffers from sample dilution anomalies and/or failure of antigen excess detection in a substantial fraction of patients. Laboratory professionals and clinicians should be alert to such analytical difficulties.
authors: Laboratory of Haematology, Universitair Ziekenhuis Brussel, Belgium. martine.vercammen@uzbrussel.be
authors: Martine
authors: M
authors: Vercammen
authors: Patricia
authors: P
authors: Meirlaen
authors: Linda
authors: L
authors: Broodtaerts
authors: Isabelle
authors: I
authors: Vande Broek
authors: Xavier
authors: X
authors: Bossuyt
mesh_terms: D015415:Biomarkers / Q000097:blood*; D006801:Humans; D007118:Immunoassay / Q000379:methods*; D007147:Immunoglobulin Light Chains / Q000097:blood*; D009391:Nephelometry and Turbidimetry / Q000379:methods*
chemical_list: D015415:Biomarkers; D007147:Immunoglobulin Light Chains