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Serum Free Light Chains

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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

The Test Sample

What is being tested?

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, or antibodies that target and neutralize specific threats to the body such as bacteria and viruses. 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 an 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 can be detected in the blood.

With a group of conditions called plasma cell disorders (dyscrasias) or monoclonal gammopathies, a plasma cell becomes malignant, dividing uncontrollably 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 produce large amounts of the same type of abnormal monoclonal immunoglobulin (M-protein). This may take the form of an intact immunoglobulin, a light chain, or rarely 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), and monoclonal light chain (primary) amyloidosis. In the beginning, these conditions may cause few symptoms, but as time progresses, they can cause bone pain and fractures, anemia, fatigue, weight loss, and kidney dysfunction.

How is the sample collected for testing?

A blood sample is obtained by inserting a needle into a vein in the arm.

NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.

Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.

Is any test preparation needed to ensure the quality of the sample?

No test preparation is needed.