The clinical significance of serum free light chains is to aid in the diagnosis of malignant plasma cell disease and to monitor treatment and recurrence of the disease. 1. Serum free light chain is an important tumor marker, which is a homogeneous κ or λ free molecule produced by the uncontrolled mass proliferation of monoclonal malignant plasma cells. It is found in the serum and urine of many malignant plasma cell diseases, such as multiple myeloma, primary systemic amyloidosis, and monoclonal gammaglobulinopathies of undetermined significance, and therefore serves as one of the indicators of auxiliary diagnosis of the diseases. 2. Serum free light chain test has high sensitivity and high specificity. In monitoring, serum free light chain assay can respond to treatment and disease recurrence earlier than other indicators. When there is a change in serum free light chain, it is recommended to consult a doctor in time to clarify the cause of the disease under the guidance of the doctor.