<prompt> M protein on immunoelectrophoresis in multiple myeloma patients is most commonly formed by -IgMIgGIgAIgD  <response>: Ans. is b i.e., IgG Immunoelectrophoresis in multiple myeloma Electrophoretic analysis permits separation of components of the serum proteins. The immunoglobulins move heterogeneously in an electric field and form a broad peak in the gamma region. The g globulin region of the electrophoretic pattern is usually increased in the sera of patients with plasma cell tumors. There is a sharp spike in this region called an M component M for monoclonal. The monoclonal antibody must be present at a concentration of at least 5 gL 0.5 gdL to be accurately quantitated by this method. This corresponds to -109 cells producing the antibody. Confirmation that such an M component is truly monoclonal and the type of immunoglobulin is determined by immunoelectrophoresis that reveals a single heavy andor light chain type. Hence immunoelectrophoresis and electrophoresis provide qualitative and quantitative assessment of the M component, respectively. The serum M component in multiple myeloma will be IgG in 53 of patients, IgA in 25, and IgD in 1; 20 of patients will have only light chains in serum and urine. 