What is Serum Free Light Chains Assay?

Also Known As: Free Light Chains, SFLC, FLC, Kappa and Lambda Free Light Chains, Quantitative Serum Free Light Chains with Ratio

Formal Name: Light Chains, Free|Free Kappa/Lambda Ratio

Light chains are proteins produced by immune cells called plasma cells. Also called kappa and lambda light chains, they link together with other proteins (heavy chains) to form immunoglobulins (also known as antibodies) that target and neutralize specific threats to the body such as bacteria and viruses. Plasma cells normally produce some excess light chains that do not combine with heavy chains and instead enter the bloodstream. Free light chains (FLC) or serum-free light chains (SFLC) refer to those that are not part of whole (intact) immunoglobulins and are present in the blood. This test measures the amount of free kappa and lambda light chains in the blood and calculates a kappa/lambda ratio to help detect, diagnose, and monitor conditions associated with increased production of free light chains.

Each type of immunoglobulin is composed of four protein chains: two identical heavy chains and two identical light chains. A particular plasma cell will produce only one type of immunoglobulin. Normally, there is a slight excess of free light chains produced, so low levels of free kappa and lambda chains are detected in the blood.

With a group of conditions called plasma cell disorders (dyscrasias) or monoclonal gammopathies, a plasma cell becomes neoplastic, dividing more than it should and producing a large number of copies (clones) of itself that crowd out other cells in the bone marrow. Since the clones come from a single plasma cell, they may produce large amounts of the same type of abnormal monoclonal immunoglobulin (M-protein). This may be an intact immunoglobulin, only a light chain, or rarely only a heavy chain.

Excess light chain production may be seen with any of the plasma cell disorders, such as multiple myeloma, MGUS (monoclonal gammopathy of unknown significance, a condition that may progress to multiple myeloma), monoclonal light chain (primary) amyloidosis, and others. These conditions may go unnoticed or may progress to produce various signs and symptoms characteristic of the different diseases.