Scand J Haematol zyx 1985;35:22-25 zyx Beta-2-microglobulin: zyxw A valuable parameter of stage, prognosis and response to treatment in myelomatosis Ole zyxwv Weis Bjerrum’ & Torben Plesner2 ’University Department of Internal Medicine and Haematology, Gentofte Hospital, Hellerup and 2Department of Medicine, The Finsen Institute, Copenhagen, Denmark zyxw Accepted for publication April 17, 1985 Berggird & Bearn isolated and described beta- 2-microglobulin (B2M) in 1968 (1). Since then a large number of studies have clarified the phys- iological characteristics and the clinical relevance of measurements of this protein. The aim of this paper is to summarize our current knowledge with special emphasis on the information that can be obtained by estimation of serum B2M in myelomatosis. B2M was first isolated from urine and found to be a single polypeptide chain of 100 amino acids of mol. wt 11 815. It was named B2M in accordance with its electrophoretic mobility (1). The complete amino acid sequence and a detailed physicochemical characterization was published a few years later (2, 3). B2M is homologous with the constant domains of IgG, the resemblance with C,H domains being particularly notable (4). It has been demon- strated that B2M is the light chain of HLA-ABC antigens (3, but the genes coding for B2M are located outside the major histocompatibility complex, on chromosome 15 (6), and no aliotypic variation has been found in man. When located at cell surface, B2M is bound to HLA-ABC antigens as the extrinsic, hydrophilic part of the complex (7). B2M is secreted from the cells and can be recovered in body fluids where 98% of B2M is in the free form, while the remainder is bound to HLA-ABC antigens (8). Serum B2M can be estimated by radioimmunoassay (9, 10). Normal serum con- centrations of B2M are presented in Table 1. The level does not undergo cyclic or diurnal varia- tions, it is unrelated to acute phase reactant proteins (12), and the turnover rate is the same in healthy individuals and in patients with myelo- matosis (13). Serum B2M increases slightly with age after adolescence, because the elimination is almost exclusively renal (14). A correlation between serum B2M and serum creatinine has been presented (15), allowing calculation of the ‘expected’ value of serum B2M at any given level of renal impairment. The ratio between measu- red and calculated serum B2M (15) or subtrac- tion of the calculated from the measured serum B2M (16) estimates the part of the serum B2M which is due to an extrarenal component. TABLE 1 Normal values mean I zy SD of serum B2M in mg/l, Evrin & Wibell zyxwvutsrqpo (11) Years Males Females B2M 17-36 1.37 I 0.20 1.40 zyxwvuts f 0.26 in myelomatosis In the period 1973 to 1980 a series of studies was carried out, determining serum B2M in a wide 37-56 1.57 ? 0.31 1.65 f 0.36 57-76 1.83 f 0.41 1.75 10.30