Patient Test Information

Beta-2 Microglobulin Tumor Marker

Also known as:

B2M; B2M; β2-Microglobulin; Thymotaxin

Formal name:

Beta2 Microglobulin, Serum, Urine, or CSF

Related tests:

Albumin, Tumor Markers, CSF Analysis

Were you looking for the Beta-2 Microglobulin test that is ordered to evaluate kidney disease?

Why Get Tested?

To help evaluate the severity and prognosis of certain cancers, including multiple myeloma and lymphoma

When to Get Tested?

When you have been diagnosed with multiple myeloma or certain other cancers; sometimes to monitor disease activity and treatment

Sample Required?

A blood sample drawn from a vein in your arm; sometimes a 24-hour urine sample; rarely a cerebrospinal fluid (CSF) sample

Test Preparation Needed?


How is it used?

This beta-2 microglobulin (B2M) test is used as a tumor marker for some 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 the health 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 ordered to assess a disease's central nervous system involvement.

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.

A CSF B2M may rarely be ordered when a health practitioner suspects that a disease such as lymphoma is affecting someone's central nervous system.

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 concentrations 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.

Increases in the CSF in someone with a disease such as HIV/AIDS indicates likely central nervous system involvement.

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.

What is being tested?

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 is 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.

NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.

Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.

Is any test preparation needed to ensure the quality of the sample?

No test preparation is needed.

  1. Should everyone have a B2M test?

    Most people will never have a B2M test done. It is not intended, or useful, as a general population screen.

  2. Can the test be done in my doctor's office?

    No, 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.

  3. 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. It may be necessary to do a blood test, a urine test, or both together. The results are not generally interchangeable.