Martine J Vercammen1, Linda Broodtaerts2, Patricia Meirlaen2, Xavier Bossuyt3. 1. Department of Hematology, Universitair ziekenhuis Brussel (UZ Brussel), Laarbeeklaan 101, Brussels 1090, Belgium; Research group: Reproductive Immunology and Implantation (REIM), Vrije Universiteit Brussel (VUB), Laarbeeklaan 103, Brussels 1090, Belgium. Electronic address: Martine.Vercammen@uzbrussel.be. 2. Department of Hematology, Universitair ziekenhuis Brussel (UZ Brussel), Laarbeeklaan 101, Brussels 1090, Belgium. 3. Laboratory Medicine, Department of Microbiology and Immunology, University Hospitals Leuven and Experimental Laboratory Immunology, KU Leuven, Herestraat 49, Leuven 3000, Belgium.
Abstract
BACKGROUND: Free light chains (FLC) are useful biomarkers for diagnosis and follow-up of plasma cell disorders. FLC quantification is encumbered by non-linearity and antigen excess (>4-fold difference between results obtained at the 2000- and 100-fold dilution). METHODS: FLC concentration was measured with Freelite® reagents on the BNII, using 100- and 2000-fold dilutions in 3645 samples. Samples displaying antigen excess were re-measured at the 2000- and/or 400-fold dilution. Carryover was evaluated by tracing samples to cuvettes and by measuring a normal sample in cuvettes that previously contained samples with a high FLC concentration. RESULTS: Antigen excess occurred in 0.93% of samples for κ and in 0.55% of samples for λ. In 81.5% of the cases, it could not be confirmed by a re-analysis of a 2000-fold and/or a 400-fold diluted sample. Real antigen excess was documented in 0.25% and 0.03% of the samples for κ and λ FLC, respectively. In the low concentration range (2000-fold dilution), imprecision was high. False antigen excess was reduced by batch analysis, introducing cleaning and rinsing procedures and using the 400-fold dilution. No antigen excess was detected in samples with normal FLC concentrations. CONCLUSION: Falsely high results occur by imprecision in the low concentration range and/or by carryover in cuvettes.
BACKGROUND: Free light chains (FLC) are useful biomarkers for diagnosis and follow-up of plasma cell disorders. FLC quantification is encumbered by non-linearity and antigen excess (>4-fold difference between results obtained at the 2000- and 100-fold dilution). METHODS: FLC concentration was measured with Freelite® reagents on the BNII, using 100- and 2000-fold dilutions in 3645 samples. Samples displaying antigen excess were re-measured at the 2000- and/or 400-fold dilution. Carryover was evaluated by tracing samples to cuvettes and by measuring a normal sample in cuvettes that previously contained samples with a high FLC concentration. RESULTS: Antigen excess occurred in 0.93% of samples for κ and in 0.55% of samples for λ. In 81.5% of the cases, it could not be confirmed by a re-analysis of a 2000-fold and/or a 400-fold diluted sample. Real antigen excess was documented in 0.25% and 0.03% of the samples for κ and λ FLC, respectively. In the low concentration range (2000-fold dilution), imprecision was high. False antigen excess was reduced by batch analysis, introducing cleaning and rinsing procedures and using the 400-fold dilution. No antigen excess was detected in samples with normal FLC concentrations. CONCLUSION: Falsely high results occur by imprecision in the low concentration range and/or by carryover in cuvettes.