English 
Italian CONTRIBUTI SCIENTIFICI – Scientific Papers
Volume:
Biochimica Clinica 2020; 44(2) 149-156
Pubblicato on-line:
January 20, 2020
DOI:
10.19186/BC_2020.012
Confronto tra un metodo nefelometrico ed un metodo turbidimetrico per la determinazione delle catene leggere libere sieriche: punti di forza e criticità
Comparison between a turbidimetric and a nephelometric method for the measurement of serum free light chains: strengths and weaknesses
AUTORI
Tommaso Trenti1
1Dipartimento Interaziendale ad Attività Integrata di Medicina di Laboratorio e Anatomia Patologica, Azienda Ospedaliera Universitaria e Azienda Unità Sanitaria Locale di Modena
ABSTRACT
Comparison between a turbidimetric and a nephelometric method for the measurement of serum free light chains: strengths and weaknesses
Background: monoclonal gammopathies include a broad spectrum of pathologies, and free light chains (FLC) measurement is recommended by guidelines for the diagnosis, follow up and prognosis of plasma cell dyscrasia. The aim of the study is to compare the measurement of FLC performed with two different analytical platforms, a nephelometer and a turbidimeter, in order to assess the analytical and diagnostic agreement.
Methods: 87 consecutive samples received by the laboratory with a request of FLC measurement were analyzed on nephelometer Immage 800 (Beckman Coulter, USA) and turbidimeter Optilite (The Binding Site, UK), using the same antibodies (Freelite, The Binding Site, UK).
Results: by applying the Passing-Bablok regression and the Bland-Altman analysis, a proportional and constant systematic error but non-significant bias for FLC ratio (rFLC) has been observed. By applying the Weighted Cohen’s Kappa (WK) test to the rFLC values, an excellent diagnostic agreement between the two instruments has been shown, considering both the normal range (0.26 – 1.65) (WK=0.87) and the diagnostic range for multiple myeloma (<0.01 or >100) (WK=0.84).
Conclusions: Although there are statistical differences between the measurements performed by the two instruments, these do not affect the diagnostic agreement, that is excellent. Nevertheless, the turbidimeter is provided with a software that can automatically detect the antigen excess; by diluting further the samples automatically, it performs fewer dilutions than the nephelometer and provides a wider range of measurement, especially for low concentrations. These characteristics assist the operator both during the analysis and the validation phases of the results, saving time and resources. On the basis of the results of the study, it can be concluded that the turbidimeter shows better performances compared to the nephelometer.