Freelite and Kloneus assays in free light chain measurements in patients with renal impairment.

BACKGROUND: Serum free light chain (FLC) quantification is a diagnostic criterion for monoclonal gammopathy and its values in patients with renal impairment are different from those in healthy subjects. The aim of this study was to evaluate Freelite and Kloneus assays in these patients. METHODS: In this retrospective study, serum samples from 226 patients with chronic kidney disease (CKD) of stages 2-5 were measured with a Freelite assay on the Optilite system and with a Kloneus assay on the AU5800 system and compared with controls without renal impairment. RESULTS: Both kappa FLC (K-FLC) and lambda FLC (L-FLC) concentrations increased with Kloneus and Freelite assays with each increment in CKD stage. In patients with CKD, Kloneus detected lower concentrations of K-FLC (median: 20.4 mg/L; 95% range: 9.8-57.2) than Freelite (median: 36.5 mg/L; 95% range: 16.5-137.7) and higher concentrations of L-FLC (median: 32.2 mg/L; 95% range: 14.4-96.7) than Freelite (median: 25.4 mg/L; 95% range: 11.9-86.0). This resulted in significantly different kappa/lambda ratios (K/L-FLC) in patients with CKD for the two tests. The Freelite K/L-FLC in the CKD group (median: 1.50; min-max: 0.66-3.45) was significantly increased compared with healthy controls, and the Kloneus K/L-FLC in the CKD group (median: 0.63; 95 % min-max: 0.34-1.01) was slightly lower. CONCLUSIONS: These findings demonstrate that Freelite and Kloneus assays provide higher but not parallel values when FLCs are measured in patients with CKD, so an increase in K/L-FLC was observed in the case of Freelite, and we found a slight decrease in the case of Kloneus.

Serum free light chain reference intervals in an Optilite and their influence on clinical guidelines.

BACKGROUND: Serum free light chain (FLC) analysis has been incorporated into the International Myeloma Working Group guidelines for the diagnosis and management of all monoclonal gammopathies. These recommendations were solely based on a single assay method (Freelite assay) and instrument. Here, we establish new reference intervals (RIs) for kappa and lambda FLC and the kappa-lambda difference and sum and a new diagnostic range for kappa/lambda FLC ratio (K/L-FLC) in an Optilite turbidimeter (The Binding Site) with the Freelite assay. METHODS: To establish new RIs, the CLSI EP28-A3C protocol was applied to 249 sample blood donors from Fuenlabrada, Spain, and the central 95% and total range were estimated. Samples from patients with polyclonal hypo- and hypergammaglobulinemia were used for the evaluation of K/L-FLC as a monoclonal proliferation index. RESULTS: The new RIs and the new K/L-FLC diagnostic range for the Optilite (0.65-2.56 mg/L) are very different from those in on the guidelines (0.26-1.65 mg/L). We propose new RIs for the K - L difference and the K + L sum. Diagnostic range validation as a monoclonal proliferation index with samples with hypo- and hypergammaglobulinemia confirms this new range. CONCLUSIONS: In this study, we present the FLC RI for Freelite reagents measured on an Optilite turbidimeter. These ranges are different from those provided by the manufacturer and from those used in most studies in the literature, which may lead to patient misclassification. Manufacturers and clinical laboratories must strive to provide RIs for the technology they are using and for their population.