Beta 2 Microglobulin (B2M) Tumor Marker Test

What is a beta-2 microglobulin tumor marker test?

A beta-2 microglobulin tumor marker test measures the amount of a protein called beta-2 microglobulin (B2M) in your body fluids. The test usually uses a sample of your blood. It may also be done using urine (pee) or in rare cases cerebrospinal fluid (CSF).

B2M is a small protein found on the surface of most cells in your body. Your cells release B2M when they are damaged or when they grow more quickly than normal. Usually, your kidneys filter B2M out of your blood. So, only small amounts of this protein are present in healthy people.

However, B2M is also a type of tumor marker. Tumor markers are substances that are often made by cancer cells or by normal cells in response to cancer. High levels of B2M in body fluids are often caused by blood and bone marrow cancers, such as:

• Multiple myeloma.
• Chronic lymphocytic leukemia (CLL).
• Certain types of lymphoma.

High B2M levels can also be caused by noncancerous conditions, such as kidney disease and autoimmune disorders. 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. Instead, it is often done after you've been diagnosed with certain cancers of the bone marrow or blood.

Other names: total beta-2 microglobulin, β2-microglobulin, B2M, B2MG, thymotaxin

What is it used for?

Though a beta-2 microglobulin tumor marker test cannot be used to screen for or diagnose cancer, it can provide valuable information about any bone marrow or blood cancer you already have. For example, testing your B2M levels can help your provider:

• Find out how much the cancer has grown or spread.
• Predict how the cancer might change (or progress) over time.
• Pick your treatment and check whether it's working. If B2M levels don't decrease during a treatment, your provider may need to adjust it.
• Check whether cancer has spread to your brain and/or spinal cord. This is done only if you have symptoms of these types of cancer.

Why do I need a beta-2 microglobulin tumor marker test?

You may need this test if you've been diagnosed with multiple myeloma, chronic lymphocytic leukemia, or certain types of lymphoma. A B2M test can help determine how serious your disease is, monitor your cancer over time, and check how well your treatment is working.

If you have multiple myeloma, a urine test for B2M may be used to see if your disease is affecting your kidneys.

What happens during a beta-2 microglobulin tumor marker 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.

For a blood test, a health care professional will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out. This usually takes less than five minutes.

For a 24-hour urine sample, you will be given a special container to collect your urine and instructions on how to collect and store your samples. Your provider will tell you what time to start. The test generally includes the following steps:

• To begin, urinate (pee) in the toilet as usual. Do not collect this urine. Write down the time you urinated.
• For the next 24 hours, collect all your urine in the container.
• During the collection period, store the urine container in the refrigerator or in a cooler with ice.
• 24 hours after starting the test, try to urinate if you can. This is the last urine collection for the test.
• Return the container with your urine to your provider's office or the laboratory as instructed.

For a cerebrospinal fluid (CSF) analysis, a provider will do a procedure called a spinal tap (also known as a lumbar puncture). A spinal tap is usually done in a hospital. A provider numbs your skin with medicine and uses a thin, hollow needle to remove some fluid from between the bones in your lower spine. You usually go home the same day.

Will I need to do anything to prepare for the test?

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.

Are there any risks to the test?

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. You may feel a little pinch or pressure when the needle is inserted. 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. The headache may last for several hours or up to a week or more. Your provider may suggest treatment to relieve the pain.

What do the results mean?

If your B2M levels were 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.
• If you have multiple myeloma, higher levels of B2M are often linked to kidney problems.

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:

• Increasing B2M levels may mean your treatment is not working.
• Decreasing B2M levels may mean your treatment is working.
• B2M levels that don't change may mean that your disease is stable and hasn't gotten better or worse.

If you have questions about your test results, talk with your provider.

Learn more about laboratory tests, reference ranges, and understanding results.

Is there anything else I need to know about a beta-2 microglobulin tumor marker test?

B2M levels may be higher than normal in many conditions that aren't cancer, including:

• Kidney disease
• HIV
• Multiple sclerosis

Because of this, providers may test your B2M levels for reasons not related to cancer treatment. These can include:

• Checking kidney function. B2M is filtered by the kidneys. So, high levels of B2M in your blood or urine may be an early sign of kidney injury.
• Monitoring immune and autoimmune diseases. Increased B2M levels may show that your immune system is more active than normal. For example, people with primary Sjogren's syndrome may have higher B2M levels in blood and even in tears.
• Detecting transplant rejection. In liver transplant patients, high B2M levels in bile and blood may be an early sign that the body is rejecting the new organ.
• Evaluating dialysis treatment. In people on long-term dialysis, B2M can build up in tissues (a condition called dialysis-related amyloidosis). Measuring B2M helps providers check how well the dialysis filter works.