Serum Free Light Chain Elevation Diagnosis

Introduction to Serum Free Light Chain Elevation

Serum free light chain elevation occurs in plasma cell disorders, lymphoproliferative disorders, monoclonal gammopathy of renal significance, and renal impairment, causing polyclonal elevation of both chains, as noted by the International Society of Nephrology 1, 2, 3

Active (symptomatic) myeloma presents with abnormal serum FLC ratio, often with an involved/uninvolved ratio ≥100 serving as a myeloma-defining event even without CRAB criteria, according to the European Society for Medical Oncology 4, 3
The American Society of Clinical Oncology recommends assessing the κ/λ ratio first when encountering elevated serum FLC, with a ratio <0.26 suggesting λ clone and a ratio >1.65 suggesting κ clone 1, 2

Waldenström Macroglobulinemia produces monoclonal IgM with associated FLC elevation, and the European Society for Medical Oncology notes that serum FLC testing is not advised in routine practice for WM as its relevance is still under evaluation 5, 1, 2
B-Cell Lymphomas and Chronic Lymphocytic Leukemia can produce monoclonal immunoglobulins with associated FLC elevation, as stated by the International Society of Nephrology 1, 2

Light Chain Cast Nephropathy requires prompt bortezomib-containing regimens to decrease nephrotoxic clonal immunoglobulin production, according to the National Kidney Foundation 3, 1, 2
Monoclonal Immunoglobulin Deposition Disease (MIDD) is associated with MM in 78-100% of cases, but only 0-20% have detectable monoclonal immunoglobulin on standard testing, as noted by the International Society of Nephrology 1, 2

Renal Impairment is the most important non-malignant cause of FLC elevation, with free light chains cleared by the kidney and impaired function causing polyclonal elevation of both κ and λ chains, according to the National Kidney Foundation 1, 2, 3
Polyclonal Immunoresponse maintains a normal or near-normal κ/λ ratio despite elevated absolute values, as stated by the American Society of Clinical Oncology 3

The European Society for Medical Oncology recommends assessing renal function and evaluating the κ/λ ratio when encountering elevated serum FLC, with a ratio 0.26-1.65 suggesting polyclonal elevation or renal impairment 1, 2, 3
The International Society of Nephrology suggests performing comprehensive protein studies, including serum and urine protein electrophoresis with immunofixation, and obtaining bone marrow evaluation if monoclonal gammopathy is suspected 4, 3

The American Society of Clinical Oncology advises never relying on serum FLC assay alone and always combining with protein electrophoresis and immunofixation, as well as using the same FLC assay for serial monitoring 3, 1, 2