Evaluation of the Impact of Renal Failure on Correlation and Concordance Between 2 Free Light Chain Assays

Caroline Moreau (1, 2) , Brice Autier (2) , Thibault Cavey (1, 2) , Emmanuel Rouger (2) , James Norwood (3) , Claude Bendavid (1, 2) , Martine Escoffre (3) , Martine Sébillot (4) , Olivier Decaux (4)

1 Foie, métabolismes et cancer
2 Laboratoire de Biochimie et Toxicologie [Rennes] = Biochemistry and Toxicology [Rennes]
3 Service d’Hématologie Clinique [Rennes]
4 Service de Médecine interne et immunologie clinique [Rennes] = internal medicine and clinical immunology [Rennes]

BACKGROUND: Free light chain (FLC) assays are essential for diagnosis and follow-up of plasma cell dyscrasia. Two assays are available: Freelite (Binding Site) and N Latex FLC (Siemens). The aim of our study was to evaluate the impact of renal failure on concordance and correlation between the 2 FLC assays. METHODS: FLC measurements using both assays were performed on 1215 fresh serum samples from patients with or without monoclonal gammopathy and renal failure. Concordance and correlation were evaluated using Passing-Bablock regression, Pearson correlation coefficient, and the Cohen kappa coefficient, taking into account the renal failure stage (evaluated with Chronic Kidney Disease-Epidemiology Collaboration formulae) and evaluation of treatment response in patients' follow-up. RESULTS: A good correlation was demonstrated between both assays, irrespective of the renal failure stage (Pearson correlation coefficient > 0.90). For FLC ratio interpretation, there remained 7.6% to 20.8% discordances between the 2 methods throughout the whole range of renal impairment. To evaluate FLC evolution in patient follow-up, 41 patients were selected with at least 6 consecutive serum samples being collected during the study period: we observed a concordant evolution of FLC concentrations between both assays. However, few discrepancies were observed with 4 patients. CONCLUSIONS: Despite adjusted reference ranges for Freelite FLC ratio, there are approximately 12.5% discrepancies in interpretation of FLC ratio between the 2 available assays. They are not linked to renal failure stage and neither of the assays performed better than the other: results must be interpreted taking into account clinical data and the same assay must be used for patient follow-up.

Mots clés: chronic kidney disease; multiple myeloma; free light chain; FLC interpretation; Monoclonal gammopathy

Domaines: Urologie et Néphrologie; Cancer

Caroline Moreau, Brice Autier, Thibault Cavey, Emmanuel Rouger, James Norwood, et al.. Evaluation of the Impact of Renal Failure on Correlation and Concordance Between 2 Free Light Chain Assays. Clinical lymphoma, 2016, 16 (12), pp.693-704. ⟨10.1016/j.clml.2016.08.012⟩. ⟨hal-01427008⟩