The value of serum free light chain in differential diagnosis of monoclonal gammopathy of renal significance

Abstract

Objective: To investigate the value of serum free light chain (FLC) in differential diagnosis of monoclonal gammopathy of renal significance (MGRS). Methods: Forty-nine hospitalized patients who underwent renal biopsy in Peking Union Medical College Hospital between January 2013 and December 2015 were included. Monoclonal gammopathy was detected by serum protein electrophoresis (SPE), serum immunofixation electrophoresis (IFE), urine IFE and serum FLC. All patients were classified as MGRS (n=32) and monoclonal gammopathy of undetermined significance (MGUS) (n=17). Results: Renal lesions in MGRS subgroup included light chain amyloidosis (n=24, 75.0%), light chain deposition disease (n=7, 21.9%), and fibrillary glomerulopathy (n=1, 3.1%). Renal diseases in MGUS subgroup included membranous nephropathy (n=10), focal segmental glomerulosclerosi (FSGS) (n=3), diabetic glomerulopathy (n=1), Henoch-Schonlein purpura nephritis (n=1), anti-GBM disease concurrent with membranous nephropathy (n=1) and glomerulomegaly (n=1). Positive number of SPE, serum IFE, urine IFE and abnormal number of serum FLC ratio in MGRS subgroup were 12, 16, 23 and 30, respectively. Positive number of SPE, serum IFE, urine IFE and abnormal number of serum FLC ratio in MGUS subgroup were 11, 17, 6 and 3, respectively. MGRS and MGUS subgroups differed significantly in positive rate of serum IFE (P<0.001), as well as positive rate of urine IFE (P=0.02) and abnormal rate of serum FLC ratio (P<0.001). The sensitivity, specificity, total consistent rate of serum FLC ratio for diagnosis of MGRS were 93.8%, 82.4%, and 89.8% respectively. The sensitivity for diagnosing MGRS could be increased to 100% by combining serum FLC ratio and urine IFE. Conclusions: The significance of monoclonal gammopathy in patients with renal disease should be evaluated by renal pathology.On the premise of excluding lymphoplasmacytic malignancy, serum FLC ratio had promising diagnostic value for MGRS, which was helpful for differential diagnosis of patients who had contraindication to renal biopsy.