MGUS is categorized into the following sub-types based upon the identity and levels of the myeloma proteins detected as well as the prognoses for progressive disease indicated by these myeloma protein findings. Non-IgM MGUS
Non-IgM MGUS, commonly termed MGUS, is diagnosed in individuals who exhibit a serum IgG, IgD, IgA, or IgE monoclonal protein with or without increased levels of blood and/or urine free κ or λ light chains. These patients typically also show small increases in bone marrow plasma cells. Further requirements for the diagnosis of non-IgM MGUS are: a) bone marrow clonal plasma cells <10% of total nucleated cells; b) absence of any of the four CRAB criteria (CRAB criteria are C = Calcium serum levels >1 milligram/deciliter above normal values and/or a serum level >11 milligram/deciliter; R = Renal insufficiency as defined by a glomerular filtration rate <40 milliliter/minute and/or a serum creatinine >2 gram/deciliter due to myeloma protein-induced kidney damaged; A = Anemia, as defined by a  blood hemoglobin level >2 gram/deciliter below normal and/or <10 gram/deciliter due to the plasma cell dyscrasia rather than e.g. iron deficiency or blood loss; B = Bone lesions, i.e. ≥1 lytic (i.e. bone re-adsorbing) bone lesion due to a plasmacytoma as detected by skeletal radiography, computed tomography, or positron emission tomography-computed tomography); c) no evidence of a plasmacytoma in bone or soft tissues, of amyloidosis, or of another plasma cell disorder; d) a ratio of free serum light chains (i.e.
multiple myeloma, Waldenström macroglobulinemia, or other B cell-associated neoplasm, that has developed, often in a stepwise manner, from their MGUS precursors.The clinical importance of understanding this spectrum of diseases is that it can be used to: a) advise individuals on the likelihood of their condition progressing to a malignant phase; b) monitor individuals for the many complications that may occur at any stage of the dyscrasias so that they can be treated to avoid or reduce their clinical impacts; and c) monitor patients for transitions to malignancy so that the malignancy can be treated at an early stage when treatment results are best. Unless otherwise noted, the advice and monitoring given here are those recommended by the International Myeloma Working Group in 2014 and updated in 2016. Clonal plasma cells
Plasma cells are key effector elements of the adaptive immune system. They contribute to immunity by making antibodies that bind with and thereby initiate the process of neutralizing specific antigens that usually are found on the surface of invading pathogens and foreign substances. Plasma cells develop from B lymphocytes (i.e. B cells) which are stimulated to undergo this maturational development by T lymphocytes during the latter cells processing of these antigens. As they are stimulated to become plasma cells, B cells refashion parts of their genome in efforts to create a new gene that encodes a functional antibody.