Beta-2 Microglobulin (B2M) Tumor Marker Test
Reviewed
Also called: Total beta-2 microglobulin, β2-microglobulin, B2MG, Thymotaxin
A beta-2 microglobulin tumor marker test measures the amount of a protein called beta-2 microglobulin (B2M) in your body fluids.
Specimen: Blood (most common), urine (24-hour collection), or cerebrospinal fluid (CSF)
Why this test may be ordered
- To find out how much a known bone marrow or blood cancer has grown or spread.
- To predict how the cancer might change over time.
- To help choose treatment and check whether it is working.
- To check whether cancer has spread to the brain or spinal cord (only if you have symptoms).
- To see if multiple myeloma is affecting your kidneys (using a urine sample).
Preparation and collection
For blood and urine tests, there are no special preparations. For a CSF analysis (spinal tap), you may be asked to empty your bladder (pee) and bowels (poop) before the test.
A beta-2 microglobulin test usually uses a sample of your blood. In certain cases, you may need to provide a 24-hour urine sample, which means collecting all your urine for a full day. If your provider suspects that cancer has spread to your brain or spine, you may have a cerebrospinal fluid (CSF) analysis.
With a blood test, there is very little risk. After the test, you may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly. With a urine test, there is no known risk. With a CSF analysis, there is very little risk from a spinal tap. After the test, you may feel some pain or tenderness in your back or have some bleeding where the needle was inserted. You may also get a headache.
Understanding results
Because high levels of B2M can be caused by such a wide variety of conditions, health care providers don't use the results from a beta-2 microglobulin tumor marker test to diagnose cancer or any other condition.
- Higher B2M levels (when measured to learn about your cancer): The higher your B2M levels, the more cancer you have in your body. Higher levels are linked to cancers that tend to grow faster. Limitation: High B2M levels can also be caused by noncancerous conditions, such as kidney disease and autoimmune disorders. Next step: If you have questions about your test results, talk with your provider.
- Increasing B2M levels during treatment: Increasing B2M levels may mean your treatment is not working. Limitation: If your B2M levels were measured to check how well your treatment is working, your provider may look at several test results over time to look for a trend. Next step: If you have questions about your test results, talk with your provider.
- Decreasing B2M levels during treatment: Decreasing B2M levels may mean your treatment is working. Limitation: If your B2M levels were measured to check how well your treatment is working, your provider may look at several test results over time to look for a trend. Next step: If you have questions about your test results, talk with your provider.
- B2M levels that don't change: B2M levels that don't change may mean that your disease is stable and hasn't gotten better or worse. Limitation: If your B2M levels were measured to check how well your treatment is working, your provider may look at several test results over time to look for a trend. Next step: If you have questions about your test results, talk with your provider.
- This test is not used to screen for or diagnose cancer.
- High B2M levels can be caused by many noncancerous conditions, including kidney disease, HIV, and multiple sclerosis.
- Results must be interpreted by a healthcare professional in the context of your full medical history and other tests.
What to do next
If you have questions about your test results, talk with your provider.
- What do my B2M levels indicate about my cancer or other condition?
- How will these results affect my treatment plan?
- Do I need to repeat this test, and if so, how often?
- Should I be concerned about any noncancerous causes of high B2M?
Evidence source
Source: U.S. National Library of Medicine (MedlinePlus). Practices and reference ranges may differ in your country.
U.S. National Library of Medicine: Beta-2 Microglobulin (B2M) Tumor Marker Test