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Beta-2-microglobulin (B2M) is a protein found on the surface of most cells and is secreted in the blood primarily by B cells (B Lymphocytes) and certain tumour cells. B2M levels are increased by anything that causes increased cell production or destruction or by any activation of the immune system. B2M levels are primarily used as a tumour marker or blood cancer marker. The results are expressed in milligrams of B2M per litre of blood (serum).

Lower levels of B2M have no clinical significance. High levels of B2M indicate a problem but cannot diagnose a specific condition. However, they do reflect the activity or significance of a cancer, if present. In an individual with multiple myeloma or lymphoma, high levels of B2M are associated with a less positive prognosis. Lower B2M levels may indicate a response to treatment for multiple myeloma. Certain drugs and conditions associated with the production or destruction of large numbers of cells (severe infections, viral infections such as CMV) or which activate the immune system (inflammation, autoimmune diseases) may also increase B2M levels.

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