Quantification of serum free light chain kappa and lambda by the SPAPLUS analyser.

OBJECTIVE Clinical assessment of the SPAPLUS® system for the determination of the serum free light chains kappa (κ FLC) and lambda (λ FLC) compared to the BNII®. DESIGN AND METHODS 126 serum specimens from our routine activity were analysed on two different analysers: the BNII® (immunonephelometry, Siemens) and the SPAPLUS® (turbidimetry, Binding Site). We compared the absolute values of the serum κ FLC and λ FLC, as well as the FLC κ/λ ratio on both analysers. These results were further evaluated together with the clinical history of the patients. RESULTS Regression analysis between the BNII® and the SPAPLUS® for κ FLC and λ FLC did not display any significant differences between both methods in the normal and pathological ranges. Nevertheless, some differences have been observed for some patients in the absolute value of the involved light chain, with potential clinical implications. CONCLUSION The results show overall good concordance between both methods. However, it is recommended that the monitoring of patients affected by monoclonal gammapathies by measuring FLC, be performed in the same laboratory and by the same method. Moreover, the FLC results should always be interpreted together with other laboratory tests taking into account the patient's diagnosis.