Introduction
Plasma cells are a type of white blood cell that helps the body fight infection. Free light chains (FLC) are proteins that are produced when plasma cells produce antibodies. Multiple Myeloma is a malignancy of the bone marrow plasma cells, where one cell starts to divide uncontrollably. As all the malignant cells are derived from the same original progenitor, the cells are described as monoclonal plasma cells. These monoclonal plasma cells secrete antibodies in the same way healthy plasma cells do, but since they come from the same plasma cell clone, they are described as monoclonal proteins. Monoclonal proteins may be intact immunoglobulins or free light chains. sFLC test measures the level of two types of free light chains, kappa (κ) and lambda (λ), in the serum and lithium heparin and EDTA plasma.1,2,3
The serum free light chain (sFLC) assay is a quantitative test used to detect the levels of free light chains in the plasma.
Why is it important?
The disorders include Multiple Myeloma (MM), intact immunoglobulin Multiple Myeloma (IIMM), light chain Multiple Myeloma (LCMM), oligo- and non-secretory Multiple Myeloma. 4,5
It also aids in the diagnosis and monitoring of AL Amyloidosis and Waldenström’s macroglobulinaemia. When used to monitor these diseases, sFLC assays can help identify response to treatments, disease progression, and relapse. 3,4,6,7,8
Freelite® assays are both CE marked, and 510k cleared.
Guidelines for monitoring
Serum FLC measurements are recommended as an aid in diagnosis and monitoring of Multiple Myeloma by the International Myeloma Working Group (IMWG), and an involved/uninvolved FLC ratio (when the involved FLC is at least 100 mg/L) is one of the "biomarkers of malignancy" to define the presence of MM. Freelite® assays are mentioned by name in these guidelines as the assay used to determine the recommended value.*
The guidelines for monitoring MM also recommend that sFLCs should be used to assess response to treatment in patients, when serum M-protein is ˂10 g/L, and urine M-protein is ˂200 mg/24 hours.9
*The decision to act when any of the SLiM biomarkers of malignancy (Bone Marrow Plasma Cells, sFLC, MRI) are the only Myeloma Defining Event, is case dependent.
It is important to note that the serum free light chain assay is not diagnostic in isolation and should be used in conjunction with other tests and clinical evaluations to confirm diagnosis.1,2,3,7,8,14
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| Definitions | |
|---|---|
| FLC | Free light chains |
| IFE | Immunofixation |
| IMWG | International myeloma working group |
| IIMM | Intact immunoglobulin multiple myeloma |
| LCMM | Light chain multiple myeloma |
| MM | Multiple myeloma |
| MGUS | Monoclonal gammopathy of undetermined significance |
| sFLC | Serum free light chains |
| SPEP | Serum protein electrophoresis |
| UPEP | urine protein electrophoresis |