A kappa light chain is one of the two types of light chains, a small piece that forms part of every antibody. Antibodies, also called immunoglobulins, are proteins made by B cells and plasma cells to fight infection. Each antibody contains either two kappa light chains or two lambda light chains, never a mix. Pathologists test for kappa and lambda light chains to find out whether a group of B cells or plasma cells is normal or abnormal.
Kappa light chain is a test result, not a diagnosis. This article explains what kappa light chains are, how pathologists test for them, and what a “kappa-restricted” result means in your pathology report.
Every antibody has four protein chains. Two are larger, called heavy chains, and two are smaller, called light chains. There are two types of light chains, kappa and lambda. Each B cell or plasma cell chooses one type as it develops and makes only that type for the rest of its life.
In a healthy person, the body contains millions of different B cells and plasma cells. Some make kappa light chains,s and some make lambda light chains, so a normal sample contains a mix of both. Normally, there are more kappa-producing cells than lambda-producing cells, usually about two to one.
Pathologists test for kappa and lambda light chains together so they can compare the results. The tests include:
Light chains can also be measured in the blood and urine. A blood test called the serum free light chain test measures the amount of kappa and lambda light chains and their ratio
Sometimes almost all of the B cells or plasma cells in a sample make kappa light chains, and very few make lambda. This result is described as “kappa-restricted” or “kappa light chain restriction.” This means the cells most likely came from a single abnormal cell that has multiplied. A group of cells that all came from one cell is called monoclonal or clonal.
A kappa-restricted result supports a diagnosis of a tumor made of B cells or plasma cells. Examples include multiple myeloma, plasmacytoma, monoclonal gammopathy of undetermined significance (MGUS), and many B-cell lymphomas. Light chain restriction alone does not tell the pathologist which condition is present.
When the sample contains a mix of kappa-producing and lambda-producing cells in roughly the normal proportion, the result is described as “polytypic” or “polyclonal.” This pattern is seen in normal tissue and in reactions to infection or inflammation. It makes a B-cell or plasma cell tumor less likely, although a small abnormal group can sometimes be hidden among many normal cells.
Both kappa-restricted and lambda-restricted results point to the same disease groups. Kappa restriction is more common overall because kappa-producing cells are more common in the body. In most conditions, whether a tumor makes kappa or lambda does not change treatment
Kappa light chains made in large amounts can pass into the urine, where they are called Bence Jones protein. They can also build up in the kidneys and damage them. Your doctor may order urine or blood tests to look for these effects.