beta-microglobulin

β-mi·cro·glob·u·lin

a polypeptide of 11,600 Da that forms the light chain of class 1 major histocompatibility antigens and can therefore be detected on all cells bearing these antigens. Free β-microglobulin is found in the blood and urine of patients with certain diseases, including Wilson disease, cadmium poisoning, and renal tubular acidosis.