Beta-2 Microglobulin Tumor Marker
When you have been diagnosed with multiple myeloma or certain other cancers; sometimes to monitor disease activity and treatment
Beta-2 microglobulin (B2M) is a protein that is found on the surface of almost all cells in the body and is shed by cells into the blood, particularly by B lymphocytes and tumor cells. It is present in most body fluids and its level rises with conditions that increase cell production and/or destruction, or that activate the immune system. This test measures B2M in the blood, urine, or rarely in the cerebrospinal fluid (CSF).
B2M is frequently elevated in the blood with cancers such as multiple myeloma and lymphoma and with inflammatory disorders and infections (e.g., HIV, CMV). Because B2M is increased with blood cell cancers, it may be useful as a tumor marker. Though it can be used to assess kidney function, this article focuses on its use as a tumor marker.
The B2M level can be increased in the CSF of individuals with blood cell cancers that have spread (metastasized) to the brain, such as lymphoma, but also with some chronic disorders such as multiple sclerosis and with viral infections such as HIV.
How is the sample collected for testing?
A blood sample is obtained by inserting a needle into a vein in the arm. A 24-hour urine sample may also be collected. Rarely, a CSF sample may be collected from the lower back using a procedure called a lumbar puncture or spinal tap.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.
How is it used?
This beta-2 microglobulin (B2M) test is used as a tumor marker for some people with blood cell cancers. It is not diagnostic for a specific disease, but it has been associated with the amount of cancer present (tumor burden) and can give a healthcare practitioner additional information about someone's likely prognosis.
A blood B2M test and sometimes a urine test may be ordered to help determine the severity and spread (stage) of multiple myeloma, to help evaluate the prognosis of cancers such as multiple myeloma and lymphoma, and may sometimes be ordered to evaluate disease activity and the effectiveness of treatment. Rarely, a CSF B2M test may be used to determine whether there is central nervous system involvement. The utility of CSF B2M in this circumstance remains unclear.
Elevated B2M in the blood is correlated with a larger amount of tumor (tumor mass) and reduced kidney function in multiple myeloma patients. Recently, the International Myeloma Working Group published new guidelines called the International Staging System for Multiple Myeloma. The staging system is based mainly off of levels of both albumin and B2M in the blood. Higher blood B2M levels correspond with higher disease stages and therefore more advanced disease with worse prognosis.
When is it ordered?
This test may be ordered during the initial workup of a person who has been diagnosed with multiple myeloma in order to stage the disease and periodically to evaluate disease activity and monitor the effectiveness of treatment. It may sometimes be ordered when a person has myeloma or lymphoma to help determine their likely prognosis.
What does the test result mean?
Increased levels of B2M in the blood and/or urine indicate that there is a problem, but they are not diagnostic of a specific disease or condition. They do, however, reflect disease activity and the amount of cancer present. When someone has been diagnosed with multiple myeloma or lymphoma, that person is likely to have a poorer prognosis if the B2M level is significantly elevated.
For monitoring treatment, decreasing levels over time in someone with multiple myeloma indicate that the person is responding to treatment. Stable or increasing levels indicate that the person is not responding.
Low levels of B2M are considered normal. B2M may be undetectable in the urine and CSF.
Is there anything else I should know?
Conditions associated with an increased rate of cell production or destruction, severe infections, viral infections such as CMV (cytomegalovirus), and some conditions that activate the immune system, such as inflammatory conditions and autoimmune disorders, can cause increases in B2M levels.
The kidneys filter wastes from the blood and reabsorb B2M. Because of this, only small amounts of B2M are normally present in the urine. If renal tubules in the kidneys become damaged or diseased, less is reabsorbed and concentrations of B2M in the urine increase (see the Beta-2 Microglobulin Kidney Disease test article).
Drugs such as lithium, cyclosporine, cisplatin, carboplatin, and aminoglycoside antibiotics can increase B2M blood and/or urine concentrations.
Recent nuclear medicine procedures and radiographic contrast media can affect test results.
How long will it take for results?
That depends on the laboratory performing the testing. The test requires specialized equipment and training and is not available in every laboratory. Your blood or urine may be sent to a reference laboratory and it may take a few days for results to be available.
What are tumor markers?
Tumor markers are substances, often proteins, that are produced by the cancer tissue itself or sometimes by the body in response to cancer growth. Because some of these substances can be detected in body samples such as blood, urine, and tissue, these markers may be used, along with other tests and procedures, to help detect and diagnose some types of cancer, predict and monitor a person's response to certain treatments, and detect recurrence.
Can I choose either a blood or a urine B2M test?
In most cases, the sample tested will be dictated by the reason that the test is being performed. For staging of multiple myeloma, a blood test is preferred. Otherwise, it may be necessary to do a blood test, a urine test, or both together. The results are not generally interchangeable.