The analytical performance evaluation of freelite™ human κ free and human λ free on the SPAPLUS™ immunoturbidimetric analyzer

Background: SPAPLUS™ is a turbidimetric immunoassay analyzer for detection of excess free light chain (FLC) antigens in serum. Here, we evaluated the analytical performance of Freelite™ Human Kappa Free and Lambda Free on a SPAPLUS™ instrument. Methods: We evaluated the precision, linearity, sample carryover, and drift of the SPAPLUS™ instrument and compared it with Hitachi 7600 and BN™ II instruments. We evaluated the detection of antigen excess for 12 specimens from patients with monoclonal gammopathy. Results: The coefficients of variations of κFLC and λFLC were below 5.0%. Linearity was shown in the range of 9.68-152.25 mg/l for κFLC and 4.96-171.09 mg/l for λFLC, and no drift was observed. The κFLC sample carryover was statistically significant, but much smaller than the optimum allowable bias. Agreement rates with the two comparative methods were 87.1, 87.1, and 97.1% or higher for κFLC, λFLC, and the κ/λ ratio, respectively. Antigen excess signals were observed for all 12 antigen excess specimens. Conclusions: The Freelite™ on the SPAPLUS™ exhibited appropriate precision, linearity, and relative comparability to the reagents on the other instruments. It was good at detecting specimens that had previously demonstrated the hook effect due to antigen excess.