β₂-microglobulin

noun

β₂-mi·​cro·​glob·​u·​lin ˌbāt-ə-ˌtü-ˌmī-krō-ˈgläb-yə-lən, chiefly British ˌbē-tə- 

: a beta globulin of low molecular weight that is present at a low level in plasma, is normally excreted in the urine, is homologous in structure to part of an antibody, comprises the light chain in certain histocompatibility antigens, and occurs at elevated levels in blood serum or urine in some pathological conditions (as tubulointerstitial disease)