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



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.



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.



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.
Laboratory of Biochemistry and Toxicology, University Hospital Center, Rennes, France; INSERM U-991, University of Rennes 1, Rennes, France. Electronic address: caroline.moreau@chu-rennes.fr.
Caroline
C
Moreau
Laboratory of Biochemistry and Toxicology, University Hospital Center, Rennes, France.
Brice
B
Autier
Laboratory of Biochemistry and Toxicology, University Hospital Center, Rennes, France; INSERM U-991, University of Rennes 1, Rennes, France.
Thibault
T
Cavey
Laboratory of Biochemistry and Toxicology, University Hospital Center, Rennes, France.
Emmanuel
E
Rouger
Department of Clinical Hematology, University Hospital Center, Rennes, France.
James
J
Norwood
Laboratory of Biochemistry and Toxicology, University Hospital Center, Rennes, France; INSERM U-991, University of Rennes 1, Rennes, France.
Claude
C
Bendavid
Department of Clinical Hematology, University Hospital Center, Rennes, France.
Martine
M
Escoffre
Department of Internal Medicine, University Hospital Center, Rennes, France.
Martine
M
Sébillot
Department of Internal Medicine, University Hospital Center, Rennes, France.
Olivier
O
Decaux
D015415:Biomarkers; D005500:Follow-Up Studies; D006801:Humans; D007074:Immunoglobulin G / Q000097:blood; D007147:Immunoglobulin Light Chains / Q000097:blood*; D007145:Immunoglobulin kappa-Chains / Q000097:blood; D007146:Immunoglobulin lambda-Chains / Q000097:blood; D007677:Kidney Function Tests; D010265:Paraproteinemias / Q000097:blood / Q000175:diagnosis; D051437:Renal Insufficiency / Q000097:blood* / Q000209:etiology / Q000652:urine; D051436:Renal Insufficiency, Chronic / Q000097:blood / Q000150:complications / Q000652:urine; D015203:Reproducibility of Results
D015415:Biomarkers; D007074:Immunoglobulin G; D007147:Immunoglobulin Light Chains; D007145:Immunoglobulin kappa-Chains; D007146:Immunoglobulin lambda-Chains
Chronic kidney disease; FLC interpretation; Free light chains; Monoclonal gammopathy; Multiple myeloma