β2-microglobulin is a kind of small molecule globulin produced by lymphocytes, platelets and polymorphonuclear leukocytes. In normal people, the synthesis rate of β2-microglobulin and its release from the cell membrane are quite constant. β2-microglobulin can be filtered freely from the glomeruli, 99.9% is absorbed in the proximal renal tubules, and is broken down in the renal tubular epithelial cells. Therefore, under normal circumstances, the excretion of β2-microglobulin is very small.