Alpha-1-Microglobulin (A1M) is a small globular protein found in all vertebrates including humans. It is synthesised in most cells of the body, mainly in the liver. It removes free radicals and oxidising agents (particularly heme) from tissues. The protein is believed to protect cells and tissues against the damage caused by reactive oxygen species or free haemoglobin. Normal urine contains traces of A1M, but in conditions with disturbed tubular function, reabsorption of A1M is reduced and increased amounts are found in urine. Therefore, A1M is a marker for renal tubular dysfunction and as a control and calibrator in various in vitro diagnostic testing kits. It can also be used as a coating antigen for ELISA or agglutination assays.