N Latex FLC serum free light-chain assays in patients with renal impairment

Background: The aim of this study was to establish ranges for N Latex free light-chain (FLC) monoclonal-based nephelometric assays in patients with renal impairment. Methods: In this retrospective study, serum samples from 284 patients with chronic kidney disease (CKD) stages 1-5 were measured with N Latex and Freelite (TM) FLC reagents on the Siemens BN (TM) II system and compared with controls without renal impairment. Results: Both kappa FLC and lambda FLC concentrations increased with the N Latex FLC and the Freelite (TM) assays with each increment in CKD stage. No difference was found in FLC kappa concentrations between the two methods. In patients with renal failure, N Latex FLC detected higher concentrations lambda FLC (CKD5 median, 128 mg/L; 95% range, 43-302) compared with Freelite (TM) (89.5 mg/L, 35-197) (p<0.0001). This resulted in significantly different kappa/lambda ratios in patients with CKD for the two tests. The Freelite (TM) kappa/lambda ratio in the CKD5 group (median, 1.22; min-max, 0.22-2.70) was significantly increased compared with healthy controls (p<0.0001), and several individual samples were outside the reference range for healthy controls (0.26-1.65). In contrast, none of the 284 patients with CKD had an FLC kappa/lambda ratio exceeding the N Latex reference limits for healthy controls (0.31-1.56). The N Latex FLC kappa/lambda ratio in the CKD5 group (0.69, 0.32-1.54) was significantly lower compared with the control group (p<0.0001). Conclusions: These findings demonstrate that the N Latex FLC kappa/lambda ratio in patients with renal failure did not differ from the reference limits for healthy controls.