Free immunoglobulin chain (FLC) analysis
Free immunoglobulin chains, also called free light chains or FLC, are formed by plasma cells in connection with the production of antibodies. They occur in two types, kappa and lambda, and circulate freely in small amounts in the blood.
The blood test measures S-FLC Kappa and S-FLC Lambda and calculates the kappa/lambda ratio. The combination of the levels and the ratio provides more information than assessing kappa or lambda separately.
What is the FLC analysis used for?
The analysis is primarily used in the investigation and follow-up of monoclonal gammopathies and plasma cell diseases, such as MGUS, multiple myeloma, light chain myeloma and AL amyloidosis. In these conditions, a group of plasma cells may produce disproportionate amounts of either kappa or lambda chains, which can result in an aberrant kappa/lambda ratio.
FLC is often used as an adjunct to serum protein fractionation, serum electrophoresis, and immunofixation. The assay may be particularly valuable when free light chains are produced without a clear M component seen with traditional protein assays.
Which markers are included?
- S-FLC Kappa – free immunoglobulin light chains of the kappa type.
- S-FLC Lambda – free immunoglobulin light chains of the lambda type.
- Kappa/Lambda ratio – shows the balance between kappa and lambda.
How is the result interpreted?
A clearly deviating kappa/lambda ratio may indicate monoclonal production of free light chains and may justify further medical investigation. If both kappa and lambda are elevated but the ratio is relatively preserved, it can instead be seen in, for example, impaired kidney function, inflammation or other polyclonal activation of the immune system.
The function of the kidneys is important in the interpretation because free light chains are mainly eliminated via the kidneys. In cases of impaired renal function, both kappa and lambda may increase without it necessarily being due to a plasma cell disease.
An abnormal FLC result is therefore not in itself a diagnosis. The result needs to be assessed together with renal function, other protein analyses and the clinical picture. In the event of clearly abnormal levels or ratios, additional investigation may be recommended.
