Abstract
AbstractBackgroundA pilot external quality assurance (EQA) survey for the free light chain (FLC) assay was developed and implemented in Korea.MethodsSurvey data over 6 years (2010–2015) were collected retrospectively and Sigma metrics were calculated for method-specific peer groups.ResultsNineteen to 29 laboratories participated in the EQA survey, and nephelometric (20%) and turbidimetric (80%) methods were used. Using a previously published clinically relevant reference change value (RCV) of 54.5% as the tolerance limit, the method-specific median Sigma metrics of kappa (κ) and lambda (λ) FLC achieved greater than Three-Sigma for 86–97% of all EQA distributions, and Five-Sigma for 48–72% of all distributions.ConclusionsThis EQA analysis of FLC assay applied clinically relevant quality specifications using Sigma metrics. During the 6-year EQA survey, we found that most of the results from participating laboratories meet clinically relevant quality specifications. In addition, method-specific differences were noted for λ FLC, at FLC concentrations above the initial measuring range that require a sample dilution.
Highlights
Free light chain (FLC) assays quantitatively measure light chains that are not bound to immunoglobulin heavy chains, and detect clonal restriction through a skewed ratio of free kappa (κ) to free lambda (λ) light chains [1].The assay uses polyclonal antibodies that bind exclusively to the hidden epitopes of free light chain (FLC) molecules located at the junction of the immunoglobulin heavy and light chains in an intact immunoglobulin
FLC achieved greater than Three-Sigma for 86–97% of all external quality assurance (EQA) distributions, and Five-Sigma for 48–72% of all distributions
During the 6-year EQA survey, we found that most of the results from participating laboratories meet clinically relevant quality specifications
Summary
The assay uses polyclonal antibodies that bind exclusively to the hidden epitopes of FLC molecules located at the junction of the immunoglobulin heavy and light chains in an intact immunoglobulin. These epitopes are only accessible when the light chain molecules are not bound to the heavy chain, which makes the assay highly specific. Technical concerns with the FLC assay include non-linearity and antigen excess, FLC polymerization, possibility of undetected “private” epitopes, lack of international standards, lot-to-lot variability of the reagent and inter-instrument variability. Survey for the free light chain (FLC) assay was developed and implemented in Korea
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