The short answer
Beta-2 microglobulin (B2M) is a small protein found on the surface of many cells. It is used as a tumor marker for multiple myeloma, chronic lymphocytic leukemia (CLL), and some lymphomas, mostly after diagnosis. Kidney disease and other conditions can also raise it, so your care team reads it in context.
Beta-2 microglobulin (B2M) is a small protein measured in blood, urine, or spinal fluid.
It is used with multiple myeloma, CLL, and some lymphomas, usually after a diagnosis.
It does not diagnose cancer by itself.
Kidney problems and some other conditions can raise B2M.
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The short version
Beta-2 microglobulin, often written B2M, is a small protein found on the surface of many cells, including lymphocytes (a type of white blood cell). Small amounts are normally found in blood and urine. Cells release it when they are damaged or grow more quickly than normal. B2M is used as a tumor marker for some blood cancers. It is not used to diagnose cancer.
What B2M is used for
The National Cancer Institute lists B2M as a marker for multiple myeloma, chronic lymphocytic leukemia (CLL), and some lymphomas. It can be measured in blood, urine, or cerebrospinal fluid (the fluid around the brain and spinal cord). After a diagnosis, care teams may use it to:
- Help understand how serious the cancer is and its likely course.
- Follow how well treatment is working.
- Check whether cancer has reached the brain or spinal cord, using a spinal fluid sample.
Why it is not read alone
The kidneys normally filter B2M out of the blood. So kidney problems can raise the level. MedlinePlus also lists other conditions that can raise B2M, including HIV, multiple sclerosis, some autoimmune disorders such as Sjögren's syndrome, and transplant rejection. That is why your care team reads B2M together with your other tests.
Normal ranges vary by lab
Your report lists a reference range, the range that lab calls normal. Labs often use different testing methods, so they often use different ranges. That means results from different labs can't always be compared directly. Your care team knows which lab ran your test and how to read your result.
What to ask
Ask why your care team is measuring B2M and how it is being used in your care. Ask whether your kidney function or another condition could affect it. Their reading of your full picture is what applies to you.
Sources
Common questions
Does a high beta-2 microglobulin mean I have cancer?
Not by itself. The kidneys normally filter B2M, so kidney disease can raise it. MedlinePlus also lists conditions such as HIV, multiple sclerosis, some autoimmune disorders, and transplant rejection. The test is used to follow known blood cancers, not to diagnose cancer.
Why is B2M checked with myeloma or lymphoma?
The National Cancer Institute lists B2M as a marker for multiple myeloma, chronic lymphocytic leukemia, and some lymphomas. It is used to help understand the likely course of the disease and to follow response to treatment. It is one piece of information among many.
Can my kidneys affect my B2M result?
Yes. B2M is filtered by the kidneys, so kidney function can affect the level. Ask your care team how they account for this in your result.
How is B2M used in my care?
Your care team may use B2M, along with other test results, to understand the cancer and follow treatment. Ask them how it is being used for you. Only your care team can explain what it means for you.
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Sources last checked: 2026-10-02 what this meansLast updated: 2026-09-27Next planned review: 2027-09-27
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Cancer Explained does not originate medical claims. Every page restates guidance already published by the National Cancer Institute, the CDC, the USPSTF and the FDA, in plain language, with the source cited so you can check the original yourself. AI does the translating and organizing; automated checks test claims, citations, clarity and safety before anything publishes, and this is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
Editorial status: Source checked — This page was written with AI assistance and then compared with the sources listed on it, looking for statements those sources do not back up. That check is not a sentence-by-sentence record and can miss errors. It is not a medical review, and it does not confirm the page is complete or right for your situation.
Human medical review: not completed. Pages here are not signed off by a clinician before they publish. That is not an oversight we are quietly working around: we restate published guidance and cite it, so the authority belongs to the source rather than to us, and every page names where its claims come from — you can verify us instead of trusting us. Where a volunteer clinician has reviewed a page, their name and credentials appear on it; where no name appears, no clinician has checked it. We are glad to have reviewers and are recruiting them, and we do not hold pages back waiting for one. Use this site to understand your situation and to ask better questions of the people treating you.
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