[The diagnostic and prognostic values of serum free light chain in patients with primary light chain amyloidosis].

Objective: To investigate the diagnostic and prognostic values of serum free light chain (sFLC) in patients with primary light chain amyloidosis (pAL). Methods: Patients diagnosed with pAL between January 2009 and June 2015 at Peking Union Medical College Hospital were included in this study to retrospectively evaluate the clinical data, sFLC, treatment and survival. Results: In total, 126 newly diagnosed pAL patients with complete sFLC data were included in this study. The median age was 57 years old (range, 37-81 years) and male to female ratio was 1.57. Eighty patients (63.5%) had lambda type light chain. Renal and cardiac involvements occurred in 87 cases (69% ) and 79 cases (62.7% ), respectively. The median value of difference between involved and uninvolved serum immunoglobulin free light chain levels (dFLC) was 99 mg/L (range, 1-4 263 mg/L). The positive rate of serum protein electrophoresis, serum immune fixation electrophoresis, urine immunofixation electrophoresis and abnormal sFLC ratio to detect monoclonal immunoglobulin were 34.9%(44 cases), 63.5%(80 cases), 77.0%(97 cases) and 81.0% (102 cases), respectively. The sensitivity for identifying monoclonal immunoglobulin could be increased to 98.4%(124 cases) by using the above-mentioned four methods. The median follow-up was 16 months, 37 patients were dead at the last follow-up. The median overall survival of all patients were not reached. Multivariate analysis showed that dFLC≥130 mg/L was independently associated with inferior survival (HR=3.272, 95%CI 1.384-7.739, P=0.007). Conclusions: Serum FLC measurement combined with other methods could improve the sensitivity of detection of monoclonal immunoglobulin in patients with pAL. The high level of dFLC was an independent prognostic factor for survival.