Valutazione delle prestazioni del sistema analitico SPAPluS per la misura della catene leggere libere del siero

Measurements of serum immunoglobulin κ and λ free light chains (FLC) and FLC ratio calculation are recommended for the evaluation of plasma cell disorders. In this study we evaluated the performance of SPAPLUS analyzer using FreeliteTM reagents (both from The Binding Site) for FLC determination. Particularly, we compared the system performance with allowable goals for bias, imprecision and total error derived from biological variation of FLC. We evaluated the SPAPLUS FLC using data collected during a 10-month period of routine use, employing three different reagent lots. The two-level (N and H) SPAPLUS control material was used for bias estimate by comparing the obtained long-term experimental means (n=54, both levels) to the corresponding manufacturer's assigned values. The protocol for CV evaluation employed the liquid-frozen Bio-Rad Liquichek unassayed chemistry control, measured in each performed run (n=48). Inaccuracy was checked by results from five UK-NEQAS exercises [system-specific (SPAPLUS) consensus value as reference]. Average cumulative bias was -1.5% (control N) and -1.4% (control H) for κ FLC, and +6.6% (N) and +6.3% (H) for λ FLC, respectively. Overall CV at physiological concentrations resulted in 10.6% for κ FLC, 8.0% for λ FLC and 9.9% for FLC ratio. On EQAS evaluation, all λ FLC, four κ FLC and three FLC ratio results were within the minimum allowable total error. Considering our previous experience with other analytical systems, the SPAPLUS solution undoubtedly represents a significant step forward. However, a further improvement in measurement imprecision is probably needed to fulfill the stringent analytical goals derived from FLC biological variation.