中倍镜显示多发性骨髓瘤的浆细胞与正常浆细胞很相似，但分化较差。通常浆细胞分化成熟，具有产生免疫球蛋白的功能。然而骨髓瘤可通过蛋白电泳中免疫球蛋白的“波峰”或者在尿液中的Bence-Jones蛋白（轻链）的存在而被检测出来。免疫电泳能有效区分产生的单克隆免疫球蛋白的类型。
At medium power, the plasma cells of multiple myeloma here are very similar to normal plasma cells, but they may also be poorly differentiated. Usually, the plasma cells are differentiated enough to retain the function of immunoglobulin production. Thus, myelomas can be detected by an immunoglobulin "spike" on protein electrophoresis, or the presence of Bence-Jones proteins (light chains) in the urine. Immunoelectrophroesis characterizes the type of monoclonal immunoglobulin being produced.
