Beta-2 microglobulin

What is being tested?
Beta-2 microglobulin (B2M) is a protein found on the surface of almost all the cells in the body. It is present in most body fluids and its blood level is raised in cancers such as multiple myeloma, leukaemia and lymphoma, and in inflammatory diseases. This test measures B2M in the blood, in the urine or, more rarely, in the cerebrospinal fluid. In the kidneys, B2M passes through the units that filter the blood, the glomeruli, and is then reabsorbed by the renal tubules, the structures that recover water, proteins, vitamins, minerals and other substances useful to the body. Normally only small amounts of B2M are found in the urine, but when the renal tubules are damaged or diseased, B2M concentrations increase because less of it is reabsorbed. In people with kidney disease who are on dialysis, B2M can form long protein chains that can be deposited in the joints and tissues, causing stiffness and pain. This condition is called dialysis-related B2M amyloidosis. B2M levels can also rise in the cerebrospinal fluid of patients with blood cancers such as leukaemia and lymphoma when these involve the brain, and also in some chronic disorders such as atherosclerosis or viral infections such as HIV.

How is the sample collected for testing?
A blood sample is taken by inserting a needle into a vein in the forearm. A 24-hour urine sample may be requested.
More rarely, a doctor may collect a sample of cerebrospinal fluid through a procedure called a lumbar puncture or through an intrathecal catheter.
No, no preparation is needed for the test.

1. How is it used?
2. When is it requested?
3. What does the test result mean?
4. Is there anything else I should know?

1. How is it used?
The characteristics of B2M make it useful as a tumour marker for some blood cancers, to detect kidney damage and to distinguish between diseases of the glomeruli and of the renal tubules. B2M is not a diagnostic test for a specific disease, but it gives the doctor further information on the prognosis of some patients and on the health of their kidneys.

• As a tumour marker: the B2M test may be requested to help determine the severity and spread (staging) of multiple myeloma and in some cases to assess the effectiveness of treatment. B2M has been associated with tumour invasiveness and tumour size and may be requested to assess the prognosis of cancers such as leukaemia and lymphoma.
• In kidney disease: B2M tests on both blood and urine may be requested together with other kidney function tests, such as creatinine and microalbumin, to assess kidney damage and to distinguish between disorders affecting the glomeruli and the renal tubules.
• The B2M test may also be requested to monitor patients who have had a kidney transplant, to detect early signs of rejection, and to monitor people exposed to high levels of cadmium and mercury, as in screening for specific occupational diseases.
Rarely, the B2M test may be requested on cerebrospinal fluid to assess whether a disease involves the central nervous system. The B2M test is not normally requested to detect or monitor dialysis-related B2M amyloidosis, inflammatory conditions or HIV infection.

2. When is it requested?
The B2M test may be requested during the initial assessment of a patient diagnosed with multiple myeloma, to monitor the disease and periodically check the effectiveness of treatment. It may also be requested when a person has leukaemia or lymphoma to help determine their prognosis.
Both blood and urine B2M tests may be requested when a person has symptoms associated with kidney dysfunction and the doctor wants to distinguish between diseases affecting the glomeruli and those affecting the renal tubules. The urine B2M test may also be requested periodically to monitor a patient who has had a kidney transplant and to monitor people exposed to high concentrations of cadmium or mercury.
A B2M test on cerebrospinal fluid may rarely be requested when a doctor suspects that a disease such as leukaemia or lymphoma affects the central nervous system.

3. What does the test result mean?
Raised B2M levels in the blood and urine indicate that something is wrong, but are not diagnostic of a specific disease or condition. They reflect tumour activity and spread, and patients with multiple myeloma, leukaemia or lymphoma are likely to have a less favourable prognosis if their blood B2M levels are considerably raised. Falling concentrations in patients with multiple myeloma indicate that the patient is responding to treatment. Rising or stable levels indicate that the patient is not responding to treatment. In people with symptoms of kidney dysfunction, raised B2M levels in the blood and reduced levels in the urine indicate that the disorder is associated with dysfunction of the glomeruli. If B2M levels are low in the blood and high in the urine, the patient probably has damage to the renal tubules. Increases in urine B2M in a patient who has had a kidney transplant may indicate early rejection of the organ. Increases in B2M levels in people exposed to high levels of cadmium or mercury may indicate early kidney dysfunction. Increases in B2M in the cerebrospinal fluid in people with diseases such as leukaemia or HIV/AIDS indicate that the central nervous system is probably involved. Low B2M levels in the blood are considered normal. B2M may be undetectable in both urine and cerebrospinal fluid.

4. 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 raise B2M levels. Medicines such as lithium, ciclosporin, cisplatin, carboplatin and aminoglycoside antibiotics can increase blood and urine B2M concentrations. Recent nuclear medicine procedures and X-ray contrast agents can affect the test results.

1. Should everyone have the B2M test?
2. Can the test be done by any laboratory?
3. Can I choose whether to have the B2M test on blood or urine?

1. Should everyone have the B2M test?
Most people will never have the B2M test. The test is not considered useful for screening the general population

2. Can the test be done by any laboratory?
No, the test requires special equipment and specially trained staff and is not available in every laboratory. Blood or urine samples may be sent to a reference laboratory.

3. Can I choose whether to have the B2M test on blood or urine?
In most cases the sample tested will depend on the reason for the test. A blood test, a urine test or both may be needed.
The results are not generally interchangeable.