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Effect of sample dilution on serum free light chain concentration by immunonephelometric assay
Martine Vercammen1, Patricia Meirlaen, Linda Broodtaerts
1Laboratory of Haematology, Universitair Ziekenhuis Brussel, Belgium. martine.vercammen@uzbrussel.be
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.
