Assessment of serum free light chain measurements in a large Chinese chronic kidney disease cohort: a multicenter real-world study

Abstract Objectives Diagnosing monoclonal gammopathy in chronic kidney disease (CKD) patients is challenging due to the complex interpretation of serum free light chain (FLC) levels. This study aimed to assess the FLC levels in a large cohort of Chinese CKD patients. Methods We enrolled 5,287 patients with all-cause nondialysis CKD from three medical centers between February 2018 and April 2023. Central 95 % reference ranges were established using data from one center and validated in an independent subpopulation from the other two centers. The crude prevalence of light chain monoclonal gammopathy of undetermined significance (LC-MGUS) was assessed against established norms for the entire cohort and subgroups based on estimated glomerular filtration rate (eGFR). Results A notable proportion of patients exceeded the standard reference limits for kappa (89.0 %), lambda (72.1 %), and FLC ratio (10.5 %), whereas non-eGFR-based renal reference interval identified only 0.3 % with abnormal FLC ratios. The iStopMM reference ranges showed higher out-of-range rates for absolute FLC levels in patients with preserved kidney function and lower rates in those with impaired kidney function, while the FLC ratio references remained robust across all groups. The crude prevalence of LC-MGUS was 10.4 % using standard ranges, predominantly kappa LC-MGUS (99.8 %). This prevalence decreased to 0.3 % with non-eGFR-based renal reference interval and 0.5 % with the iStopMM ranges. Using the newly established reference ranges, the crude prevalence was found to be 0.9 %. Conclusions Our findings suggest that current FLC reference ranges are inadequate for the Chinese population, underscoring the need for eGFR-based reference ranges tailored to this demographic.