RESUMEN
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.