At a glance

Also known as

B2M; β2-Microglobulin; Thymotaxin

Why get tested?

To help evaluate the severity and prognosis of multiple myeloma, leukaemia, or lymphoma; to distinguish between kidney disorders; and to detect kidney damage

When to get tested?

When you have been diagnosed with multiple myeloma or certain other cancers; sometimes to monitor treatment; when you have signs associated with kidney dysfunction

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?


What is being tested?

Beta2-microglobulin (B2M) is a protein that is found on the surface of almost all cells in the body. It is present in most body fluids and is increased in the blood with cancers such as multiple myelomaleukaemia and lymphoma, and with inflammatory disorders. This test measures B2M in the blood, urine or rarely, in the cerebrospinal fluid (CSF).

In the kidneys, B2M passes through blood filtering units, the glomeruli, and is then reabsorbed by the renal tubules - these are structures that reclaim water, proteins, vitamins, minerals and other substances that are useful to the body. Normally, only small amounts of B2M are present in the urine but when the renal tubules become damaged or diseased, concentrations increase due to a decrease in resorption. In people with kidney disease who are undergoing dialysis, B2M can form long protein chains that can be deposited in joints and tissues, causing stiffness and pain. This condition is called B2M dialysis-associated amyloidosis.

B2M levels can be increased in the CSF of patients with blood cell cancers involving the brain, such as leukaemia and 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 can also be collected. Rarely, a CSF sample can be collected by a doctor from the lower back using a procedure called a lumbar puncture or spinal tap.

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

No test preparation is needed

The Test

How is it used?

The characteristics of beta2 microglobulin (B2M) make it useful as a tumour marker for some blood cell cancers, for detecting kidney damage and for distinguishing between glomerular and tubular disorders of the kidney. B2M is not diagnostic for a specific disease but rather it gives additional information about someone's likely prognosis and about the health of their kidneys.

  • As a tumour marker: a blood B2M test may be ordered to help determine the severity and spread (stage) of multiple myeloma and may sometimes be ordered to evaluate the effectiveness of treatment. B2M has been associated with tumour burden, the amount of cancer present, and it can be ordered to help evaluate the prognosis of cancers such as leukaemia and lymphoma.
  • In kidney disease: both blood and urine B2M tests can be ordered along with other kidney function tests such as ureacreatinine, and albumin/creatinine ratio to evaluate kidney damage and disease and to distinguish between disorders that affect the glomeruli and the renal tubules. B2M tests can sometimes be ordered to monitor people who have had a kidney transplant, to detect early signs of rejection, and ordered to monitor people who are exposed to high levels of cadmium and mercury, such as in the case of occupational exposure.

Rarely, a CSF B2M test can be ordered to assess a disease's central nervous system involvement. The B2M test is not typically ordered to detect or monitor B2M dialysis-related amyloidosis, to monitor inflammatory conditions, or to monitor HIV.

When is it requested?

A B2M 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 monitor the effectiveness of treatment. It may sometimes be ordered when a person has leukaemia or lymphoma to help determine their likely prognosis.

Both blood and urine B2M tests may be ordered when a person has symptoms associated with kidney dysfunction and the doctor wants to distinguish between disorders that affect the glomeruli and the renal tubules. A urine test may also be ordered periodically to monitor a person who has had a kidney transplant and to monitor those exposed to high concentrations of cadmium or mercury.

CSF B2M may rarely be ordered when a doctor suspects that a disease such as leukaemia or lymphoma is affecting the central nervous system.

What does the test result mean?

Increased levels of B2M in the blood and urine indicate that there is a problem, but they are not diagnostic of a specific disease or condition. They do reflect disease activity and tumour burden, and when a person has been diagnosed with multiple myelomaleukaemia, or lymphoma, they are likely to have a poorer prognosis if their blood B2M levels are significantly elevated. Decreasing concentrations in someone with multiple myeloma indicate that a person is responding to treatment. Stable or increasing levels indicate that the person is not responding.

In someone with signs of kidney disease, increased levels of B2M in the blood and low levels in the urine indicate that the disorder is associated with glomerular dysfunction. If B2M is low in the blood and high in the urine, then it is likely that the person has renal tubule damage or disease. Increases in urine B2M in a person with a kidney transplant may indicate early kidney rejection. Increases in someone who is exposed to high levels of cadmium or mercury may indicate early kidney dysfunction.

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

Low levels of B2M are considered normal. B2M may be undetectable in the urine and CSF.

About Reference Intervals

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.

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.

Common Questions

Should everyone have a B2M test?

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

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

No, the test requires specialised equipment and training and is not available in every laboratory. Your blood or urine may be sent to a reference laboratory.

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.

Last Review Date: July 9, 2016