Renal Function Status Influences Serum Free Light Chain Concentrations And Diagnostic Performance

Quantitative analyses of serum free light chain(FLC)have been confirmed to be a sensitive and critical assay in identifying monoclonal gammopathy.At present,the reference range is mainly based on foreign literatures,lacking of large sample data in Chinese patients with kidney disease.As renal dysfunction worsens,serum FLC concentrations change,and the diagnostic performance of κ/λ ratio becomes controversial.A total of 2,711 patients who were hospitalized at the National Clinical Research of Kidney diseases in Jinling Hospital Affiliated to Nanjing University School of Medicine who have been tested for serum FLC were incorporated into observation,in which there were 278 monoclonal gammopathy patients and 2433 other patients.Clinical and laboratory data were retrospectively analyzed to measure the reference range of serum FLC in Chinese patients with kidney disease,and to explore its diagnostic value and clinical application in monoclonal gammopathy.Both κFLC and XFLC were positively correlated with serum creatinine and cystatin C,and negatively correlated with eGFR,with cystatin C the strongest.κ/λ has the same correlations,but is strongly correlated with eGFR(correlation coefficient-0.34,P<0.01).Reference ranges of κFLC(10.75～68.22mg/L),λFLC(12.16～50.29mg/L),and κ/λ(0.49～1.93)were set in patients with normal renal function and excluded for autoimmune disease or infection(all 95%confidence intervals).In patients with all kinds of renal status,the range of κFLC was 11.10-152.89mg/L,XFLC was 12.20～118.53mg/L,κ/λ was 0.52～2.36.Renal dysfunction influences the diagnostic performance of κ/λ.From normal to extremely impaired renal function group,the specificity of κ/λ decreased stepwise.A classification method based on renal function,was proved to have an optimal diagnostic performance over all ranges with an AUC of 0.880.specifically,when patient’s eGFR was no less than 90 mL/(min·1.73 m2),we use 0.49～1.93 as the diagnostic range,otherwise,we use 0.52～2.36 as the diagnostic range.The sensitivity of this method varied in different types of monoclonal gammopathy.In conclusion,with the progression of renal dysfunction,serum FLC concentrations and κ/λ elevated,affecting the diagnostic performance of κ/λ for monoclonal gammopathy.Patients with chronic kidney disease should use different diagnostic ranges according to different renal function status.The application of center-specific diagnostic ranges can improve the diagnostic performance.