This page was reviewed under our medical and editorial policy by
Bradford Tan, MD, Chair, Department of Pathology and Laboratory Medicine, City of Hope Atlanta, Chicago and Phoenix
This page was updated on June 8, 2023.
Beta-2 microglobulin (B2M) is a biomarker protein found on the surface of cells, including lymphocytes, and in bodily fluids. B2M is considered a tumor marker because high levels of the antigen may be indicative of certain cancers.
In normal biological functioning, B2M is synthesized, excreted and reabsorbed back into the body. In certain diseases, B2M is absorbed less efficiently or produced more quickly, increasing the amount in the blood.
B2M tests aren’t used to diagnose cancer, but rather as an investigational tool during diagnosis and to help follow changes in a disease after diagnosis. This article will explore the following topics:
B2M tumor marker tests are typically used after the patient has a confirmed diagnosis. A B2M test is used to track the progression of cancer and how it responds to treatment and to predict how cancer will develop.
B2M tumor marker tests are usually performed by taking a sample of the patient’s blood, but sometimes urine and cerebrospinal fluid are used, depending on the type of cancer.
Elevated levels of B2M in bodily fluids may be associated with certain cancers of the blood and bone marrow, such as myeloma, chronic lymphocytic leukemia (CLL) and a few types of lymphoma.
A B2M tumor marker test may be first used for investigation purposes following initial diagnosis to help guide early treatment. Once treatment is underway, a B2M test may then be used to check whether cancer has spread to the brain and/or spinal cord. After treatment, additional B2M tests may be used to confirm whether cancer has returned or spread since treatment stopped.
A healthy person synthesizes 150 to 200 milligrams (mg) of B2M a day, which amounts to a small concentration of 1.5 to 3 mg per liter (mg/L) of blood serum.
Concentrations in urine tests for healthy people are even lower, typically about 0.04 to 0.22 mg/L, with higher concentrations pointing to conditions that directly impact the kidneys.
Concentrations found in cerebrospinal fluid have a wider range than the other two at 0.2 to 2 mg/L in healthy people. Cerebrospinal fluid is less likely to be affected by problems with other organ systems, so it’s a more precise measure for cancers of the brain and spinal cord.
Patients diagnosed with multiple myeloma, CLL or certain types of lymphoma have been found to have elevated B2M levels. Other noncancerous conditions may impact B2M levels as well.
Patients with known blood and bone marrow cancers may have multiple B2M tumor marker tests during the course of treatment, because antigen levels change in response to disease progression or regression. Increasing B2M levels may suggest cancer has grown, while decreasing levels may indicate the cancer is responding to treatment.
Elevated levels in a multiple myeloma patient may suggest kidney disease.
A B2M tumor marker test is a valuable tool for the monitoring and treatment of certain cancers. Health care providers may use B2M levels to understand whether treatment is working or whether different options should be considered. The patient’s cancer care team will discuss test results and how they affect the treatment plan and prognosis.