The presence of M protein in the blood does not necessarily indicate myeloma, but of course M protein plays an important role in the identification of myeloma. Multiple myeloma is the most common malignant plasma cell disease in which monoclonal plasma cells proliferate tumorigenically in the bone marrow, producing a large number of monoclonal immunoglobulins, mainly M protein, and leading to multiple osteolytic lesions, which can lead to bone pain, bone fracture, anemia, hypercalcemia, renal damage, and a high susceptibility to infections as the main clinical manifestations. The minimum criteria for the diagnosis of multiple myeloma are smear plasma cells in the bone marrow >10% or the presence of a plasmacytoma plus one of the following conditions, such as serum M protein >30 g/L, presence of M protein in the urine, and osteolytic lesions.