Blood
Serum Free Light Chains (Kappa)
Also known as: Free Kappa, Kappa FLC
Reference ranges by source
Published adult intervals: 2, from 2 named sources, shown in mg/L.
About Serum Free Light Chains (Kappa)
A free light chains test measures the level of free light chains in your blood. Light chains are proteins made by plasma cells, a type of white blood cell. Light chains usually link up with other proteins called heavy chains. Together, the light and heavy chains make immunoglobulins, also called antibodies. Antibodies are proteins that your immune system makes to fight germs such as viruses and bacteria.
Light chains can be either bound to heavy chains or free in the blood.
There are two types of light chains: lambda and kappa light chains. You will usually have some of each in your blood. A free light chains test measures the amount of lambda and kappa free light chains in your blood.
If the amount of free light chains is higher or lower than normal, it may be a sign of a disorder of the plasma cells. These disorders include multiple myeloma, a cancer that begins in the plasma cells, and amyloidosis, a condition that occurs when abnormal proteins build up and collect in different organs and tissues.
Main source: MedlinePlus ↗
Useful for
Measure free kappa light chains in your blood, alongside lambda, and compare them as a kappa-to-lambda ratio.
Help find or follow plasma cell disorders that mainly produce kappa light chains, such as some types of multiple myeloma, AL amyloidosis, light-chain deposition disease, and non-secretory myeloma.
Help diagnose plasma cell disorders that don't show up on standard blood or urine protein tests.
Help follow how well treatment for these disorders is working over time, since changes in kappa free light chains can show whether the abnormal plasma cells are growing or shrinking.
Main source: MedlinePlus ↗
Interpretation
Your results will show the amounts of lambda and kappa free light chains in your blood. They will also provide a comparison between the two, called a ratio.
A high kappa free light chain level along with a high kappa-to-lambda ratio suggests that one type of plasma cell is making too much kappa light chain, which can be a sign of a plasma cell disorder.
If both kappa and lambda are high but the ratio is normal, this often means the immune system is being broadly stimulated, such as in some chronic infections or autoimmune diseases.
Kidney problems can also raise free light chain levels because the kidneys normally clear them out. In this case, the kappa-to-lambda ratio is more useful than the kappa value alone.
To understand the results of a free light chains test, your provider will consider your symptoms, medical history, and the results of other blood tests, such as serum and urine protein electrophoresis.
For general wellness information only. Talk to a clinician about your specific results.
Main source: MedlinePlus ↗
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Sources
Last updated 2026-05-02
This page presents source-specific reference data and sourced explanations. For general wellness information only. This is not medical advice. For diagnosis or treatment of any condition, talk to a qualified clinician.