Beta-2 Microglobulin (B2M) Tumor Marker Test

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, no special preparations are needed. For a CSF analysis (spinal tap), you may be asked to empty your bladder and bowels before the test.

For a blood test, a small needle is used to take a sample from a vein in your arm. For a 24-hour urine sample, you collect all your urine over a full day into a special container and store it in the refrigerator or a cooler with ice. For a CSF analysis, a spinal tap (lumbar puncture) is performed in a hospital.

With a blood test, there is very little risk; you may have slight pain or bruising at the needle site. With a urine test, there is no known risk. With a CSF analysis, there is very little risk; you may feel a pinch or pressure, and afterward you may have back pain, bleeding at the needle site, or a headache that can last from several hours to a week or more.

Understanding results

Your healthcare provider will interpret your B2M results based on your specific situation. The following patterns are general guidelines.

• Higher B2M levels: May indicate more cancer in the body, a faster-growing cancer, or kidney problems (especially in multiple myeloma). Noncancerous conditions such as kidney disease, HIV, or multiple sclerosis can also cause higher levels. Limitation: This test cannot diagnose cancer or any other condition. High levels have many possible causes, and your provider will consider other tests and your overall health. Next step: Your provider will discuss what the results mean for your specific condition and may adjust your treatment or order additional tests.
• Lower B2M levels (or decreasing levels over time): May indicate that treatment is working and the cancer is responding. Limitation: Levels can vary due to kidney function and other factors. A single low result does not confirm that the cancer is gone. Next step: Your provider will monitor your levels over time to see the trend and decide if treatment should continue or change.
• Stable B2M levels (no significant change over time): May indicate that the disease is stable and has not gotten better or worse. Limitation: Stable levels do not guarantee that the cancer will not progress in the future. Next step: Your provider will continue to monitor your levels and overall condition.

• 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. They can explain what your B2M levels mean for your specific situation and treatment plan.

• 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

U.S. National Library of Medicine: Beta-2 Microglobulin (B2M) Tumor Marker Test