Interlaboratory study of free monoclonal immunoglobulin light chain quantification.

BACKGROUND: Quantification of monoclonal immunoglobulin free light chains (FLCs) in serum is used increasingly in clinical practice for the diagnosis, prognostic assessment, and treatment monitoring of monoclonal gammopathies. It is used as an adjunct to standard serum protein electrophoresis and immunofixation. However, methods for FLC quantification need further standardization and validation. METHODS: The Czech Myeloma Group and the Czech Society of Clinical Biochemistry have initiated an interlaboratory study where six laboratories collaborating with the primary myeloma treatment centres measured FLC concentrations in 12 serum samples from patients with monoclonal gammopathies. RESULTS: Repeatability of the measurements in five laboratories was calculated based on differences between the results of duplicate measurements. We found that repeatability depended more on the laboratory than on the device used for measurement. CONCLUSIONS: The study revealed several weak points in the methodology, including the need for a uniform sample dilution procedure. Interlaboratory reproducibility was comparable with values achieved in the NEQAS programme. Because the κ/λ ratio cannot be measured with high precision, κ and λ FLC concentrations should be used where possible. Due to its impact on the clinical management of patients with gammopathy, FLC quantification needs to become a part of the regular quality control cycle in myeloma centres.

Comparability of eight immunoassay procedures for the determination of CA 15-3 and related markers.

MUC1 mucins are tumour markers that are frequently indicated and examined, particularly as part of the treatment of breast cancer. Relatively large differences were observed in external quality assessment (EQA) between the results that were obtained by different immunoassay technologies. Thus, we compared eight routinely employed immunoassay sets for the determination of MUC1 mucins in the serum: six closed automated systems (AxSYM, Centaur, ECi Vitros, Elecsys 2010, Immulite 2000 and Kryptor), and two IRMA kits (ELSA CIS and IRMA-mat Byk-Sangtec). Using all analytical systems, we measured identical groups of clinical samples complete with selected calibrator and control samples. The repeatability of measurements (presented as coefficients of variation) ranged from 0.7% (Kryptor) to 6.9% (Immulite 2000). Even though the cut-off values differ among various systems, no similar clinical efficacy appears to be attained. In the region of cut-off values, the highest specificity that was set as a standard was found for the AxSYM analyser, while the sensitivity was highest for the Elecsys 2010. Data from Bland-Altman differential plots suggest the presence of significant individual differences among individual samples, mainly in the region of high concentrations of MUC1 mucins. The parameters of Passing-Bablok regression show significant systematic differences between some of the analytical systems as well as an increase of the differences with increasing MUC1 mucin concentrations. The effect of the combination of antibodies used on the extent of differences among results obtained with individual systems is more obvious than the effect of the matrix of analysed materials.