The Evaluation of Light Chains USING ELISA Method

Introduction: Free light chain assay (FLC) has moved into clinical practice based on the building evidence of its utility in multiple myeloma (MM) and other monoclonal gammopathies. The purpose of the study is to verify the effectiveness of the basic parameters relevant to serum free light chain analysis using ELISA method and to compare it with the well-established FreeLite assay.

Methodology and sample collection: ELISA method was tested using diagnostic kit developed by Biovendor (Czech Republic). Immunoturbidimetric measurement using the FreeLite kit (The Binding Site), adapted on the Modular P (Roche), and was used as a reference method. Regression analysis, developed by Passing and Bablok, expressed by equation Y = −9,84 + 1,53 X allowed to compare the two methods. In total, the results of serum FLC determination in 40 donors and in 202 patients with monoclonal gammopathies were compared.

Results: Reference intervals were tentatively determined based on an analysis of male and female blood donor samples. The ratio kappa/lambda was from 0.24 to 1.17 by use of ELISA method and from 0.53 to 1.92 by reference immunoturbidimetric method. Intermediate measurement precision was obtained as follows: (intermediate) kappa using ELISA 6,6–11,0 %, using immunoturbidimetric method 5,6–6,9 %; lambda using ELISA 7,3–8,6 %, using immunoturbidimetric method 6,1–9,2 %. Regression coefficient was R = 0, 73. We were observing the influence of sample dilution on the results and we confirmed the necessity to verify the degree of dilution in each pathologically changed sample. The main factors of a successful free light chain determination are: validity of the reference intervals, difference in diagnostic classification when using different methods. Considering the necessary dilution, every patient sample requires a special and individual attention. In many patients, an applicable result can be obtained only having repeated the measurements at different dilution levels; therefore, it is not possible to predict the number of examinations one kit can serve to.

Conclusion: The determination of serum free light chains cannot be considered as a routine procedure for the time being. This analysis requires careful sample preparation and high professional level of laboratory personal. Both methods used to determine serum FLC are suitable for laboratory practice; the comparability of their predictive value in clinical practice requires a further testing.