Immunoglobulin kappa constant, also known as IGKC, is a gene that encodes the constant domain of kappa-type light chains for antibodies. The immunoglobulin light chain is the small polypeptide subunit of an antibody （immunoglobulin）. A typical antibody is composed of two immunoglobulin （Ig） heavy chains and two Ig light chains. kappa （κ） chain is one of the two types of light chain in humans. A free light chains test measures the amount of lambda and kappa free light chains in the blood. If the amount of free light chains is higher or lower than normal, it can mean you have a disorder of the plasma cells. These include multiple myeloma, a cancer of plasma cells, and amyloidosis, a condition that causes a dangerous buildup of proteins in different organs and tissues.