This is the first of four installments in a series covering investigative tools used for diagnosing multiple myeloma.

The diagnostic work-up for detecting multiple myeloma traditionally includes: (1) confirmation of the expansion of clonal plasma cells, or a group of plasma cells; (2) evaluation of organ damage ^[1]; and (3) determination of possible factors that may affect therapy and long-term outcome ^[2]. This article will touch on clonal plasma cell expansion.

Clonal plasma cell expansion is an abnormal increase in the proliferation of a group of immature plasma cells. It is verified by testing for the presence of an antibody called monoclonal immunoglobulin protein (M-protein). An excess of M-protein is what leads to multiple myeloma.

An initial laboratory evaluation detects and quantifies the amount of M-protein in the blood and urine using a technique called serum protein electrophoresis. Serum protein electrophoresis applies an electric current to a sample of blood serum. This separates the serum’s proteins into five groups based on size and electric charge. The groups can tell physicians about what proteins are in the blood and potentially point to a diagnosis of multiple myeloma.

Another test physicians use is a serum free light chain assay (SFLC). Antibodies, including M-proteins, are made up of two light chains and two heavy chains. The chains are called free chains when they are secreted independently, and patients with myeloma have abnormally high levels of free light chains. SFLC measures the amount of specific free light chains in serum and has become an important tool for tracking response to therapy as well as disease progression.

Bone marrow is also examined for the presence of clonal plasma cells. Looking at bone marrow helps physicians differentiate between myeloma cells and normal plasma cells in a given patient, and certain external features of the cells may suggest aggressive disease. However, while both number and clonal nature of the plasma cells are important, myeloma cells can vary in appearance both among and within myeloma patients.

For more information about diagnostic criteria for multiple myeloma, see the full article in the American Society of Hematology’s 2008 Education Program Book, Hematology ^[3].  For more information about the serum free light chain assay, see a related Myeloma Beacon article ^[4].