Beta-2 Microglobulin (B2M)
Beta-2 microglobulin (B2M) is a small protein found on the surface of most cells and released into the blood as cells are naturally renewed. The test measures its level in blood, and sometimes in urine or spinal fluid.
B2M is used mainly to help monitor certain known conditions and to assess kidney function, since the kidneys clear this protein from the blood. It is not a stand-alone screening or diagnostic test. Its value is best understood as one input a clinician weighs alongside your kidney health and overall picture.
A raised B2M is not a diagnosis and is very often related to how well your kidneys are filtering, since reduced kidney function alone can elevate it. Inflammation, infections including common viral illnesses, and other immune-active states can also increase it. Your clinician interprets B2M together with kidney markers and your broader clinical context rather than on its own.
A low or normal B2M is generally unremarkable and is the common finding in healthy people with normal kidney function. It simply reflects typical cell turnover and clearance.
There is no universal target, because the meaningful range depends heavily on your kidney function and why the test was ordered. A clinician should interpret B2M in that context rather than against a generic number.
Sources
Educational context only, not medical advice or a diagnosis. Reference ranges vary by lab, age and sex; always discuss your results with a clinician.