Variabilità biologica delle catene leggere libere delle immunoglobuline nel siero

The measurement of serum κ and λ free light chains (FLC) and κ/λ FLC ratio calculation are recommended for screening, prognostic evaluation and monitoring of multiple myeloma and related plasma cell disorders. Given the lack of reliable data available in literature, in this study we assessed biologic variability components of FLCs and FLC ratio by an accurately designed protocol. We collected five blood specimens from each of 21 healthy volunteers (9 men and 12 women; age range, 23-54 years) on the same day, every two weeks for two months. Serum specimens were stored at -80° C until analysis and analyzed in a single run in duplicate using a SPAPLUS immunoturbidimetric platform and Freelite reagents (The Binding Site). Data were analyzed by ANOVA. Serum λ FLC concentrations were significantly (P <0.01) higher in men. The inter-individual variance of λ FLC was higher than that of κ FLC. Within- and between-subject CVs were 8.1% and 14.1% for κ FLC, 7.0% and 27.5% for λ FLC, and 4.5% and 15.3% for FLC ratio. All parameters had marked individuality showing that the use of population-based reference intervals could be inadequate for test interpretation. The reference change value was between 20% and 30% depending from the assay imprecision. Desirable analytical goals for imprecision (CV), bias and total error were <4.0%, ±4.1% and ±10.7% for κ FLC, <3.5%, ±7.1% and ±12.9% for λ FLC, and <2.3%, ±4.0% and ±7.7% for FLC ratio.