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.

A free light chains test is used to measure the level of free light chains in the blood and compare the amount of kappa and lambda light chains. This ratio can help diagnose or monitor how well the treatment of plasma cell disorders is working.

Source: MedlinePlus, U.S. National Library of Medicine