Analysis of a 6-year pilot external quality assurance survey of free light chain using Sigma metrics

Background: A pilot external quality assurance (EQA) survey for the free light chain (FLC) assay was developed and implemented in Korea. Methods: Survey data over 6 years (2010-2015) were collected retrospectively and Sigma metrics were calculated for method-specific peer groups. Results: Nineteen 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 (kappa) and lambda (lambda) FLC achieved greater than Three-Sigma for 86-97% of all EQA distributions, and Five-Sigma for 48-72% of all distributions. Conclusions: This 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 lambda FLC, at FLC concentrations above the initial measuring range that require a sample dilution.