• Also Known As:
  • B2M
  • B2M
  • β2-Microglobulin
  • Thymotaxin
  • Formal Name:
  • Beta2 Microglobulin
  • Serum
  • Urine
  • or CSF
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At a Glance

Why Get Tested?

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

Were you looking instead for Beta-2 Microglobulin for Kidney Disease?

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?


You may be able to find your test results on your laboratory’s website or patient portal. However, you are currently at Lab Tests Online. You may have been directed here by your lab’s website in order to provide you with background information about the test(s) you had performed. You will need to return to your lab’s website or portal, or contact your healthcare practitioner in order to obtain your test results.

Lab Tests Online is an award-winning patient education website offering information on laboratory tests. The content on the site, which has been reviewed by laboratory scientists and other medical professionals, provides general explanations of what results might mean for each test listed on the site, such as what a high or low value might suggest to your healthcare practitioner about your health or medical condition.

The reference ranges for your tests can be found on your laboratory report. They are typically found to the right of your results.

If you do not have your lab report, consult your healthcare provider or the laboratory that performed the test(s) to obtain the reference range.

Laboratory test results are not meaningful by themselves. Their meaning comes from comparison to reference ranges. Reference ranges are the values expected for a healthy person. They are sometimes called “normal” values. By comparing your test results with reference values, you and your healthcare provider can see if any of your test results fall outside the range of expected values. Values that are outside expected ranges can provide clues to help identify possible conditions or diseases.

While accuracy of laboratory testing has significantly evolved over the past few decades, some lab-to-lab variability can occur due to differences in testing equipment, chemical reagents, and techniques. This is a reason why so few reference ranges are provided on this site. It is important to know that you must use the range supplied by the laboratory that performed your test to evaluate whether your results are “within normal limits.”

For more information, please read the article Reference Ranges and What They Mean.

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 may be 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.

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

No test preparation is needed.


Common Questions

How is it used?

This beta-2 microglobulin (B2M) test is used as a tumor marker for some people with 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 a healthcare 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 used to determine whether there is central nervous system involvement. The utility of CSF B2M in this circumstance remains unclear.

Elevated B2M in the blood is correlated with a larger amount of tumor (tumor mass) and reduced kidney function in multiple myeloma patients. Recently, the International Myeloma Working Group published new guidelines called the International Staging System for Multiple Myeloma. The staging system is based mainly off of levels of both albumin and B2M in the blood. Higher blood B2M levels correspond with higher disease stages and therefore more advanced disease with worse prognosis.

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 healthcare 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 levels 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 indicate 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.

How long will it take for results?

That depends on the laboratory performing the testing. 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 and it may take a few days for results to be available.

What are tumor markers?

Tumor markers are substances, often proteins, that are produced by the cancer tissue itself or sometimes by the body in response to cancer growth. Because some of these substances can be detected in body samples such as blood, urine, and tissue, these markers may be used, along with other tests and procedures, to help detect and diagnose some types of cancer, predict and monitor a person’s response to certain treatments, and detect recurrence.

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. For staging of multiple myeloma, a blood test is preferred. Otherwise, it may be necessary to do a blood test, a urine test, or both together. The results are not generally interchangeable.

View Sources

Sources Used in Current Review

2017 review performed by Allison B. Chambliss, PhD, DABCC, FACB, Scientific Director, LAC+USC Medical Center Core Laboratory.

(November 4, 2015) Tumor Markers. NIH National Cancer Institute. Available online at https://www.cancer.gov/about-cancer/diagnosis-staging/diagnosis/tumor-markers-fact-sheet. Accessed on 4/10/17.

(January 19, 2016) How Is Multiple Myeloma Staged? American Cancer Society. Available online at https://www.cancer.org/cancer/multiple-myeloma/detection-diagnosis-staging/staging.html. Accessed on 4/10/17.

Palumbo et al. Revised International Staging System for Multiple Myeloma: A Report From International Myeloma Working Group. Journal of Clinical Oncology 33, no. 26 (September 2015) 2863-2869. Available online at http://ascopubs.org/doi/full/10.1200/jco.2015.61.2267. Accessed on 4/10/17.

Jadeja N, Nalleballe K, Graber, J. Pearls & Oy-sters: Plasma cell meningitis: An uncommon complication of multiple myeloma. Neurology 87, no. 20 (November 2016) e240-e242. Available online at https://www.ncbi.nlm.nih.gov/pubmed/27906664. Accessed on 4/10/17.

Teitz Clinical Guide to Laboratory Tests. Wu AHB, ed. 4th Edition: St. Louis: Elsevier Saunders.

Sources Used in Previous Reviews

Pagana, K. D. & Pagana, T. J. (© 2007). Mosby’s Diagnostic and Laboratory Test Reference 8th Edition: Mosby, Inc., Saint Louis, MO. Pp 155-156.

Wu, A. (© 2006). Tietz Clinical Guide to Laboratory Tests, 4th Edition: Saunders Elsevier, St. Louis, MO. Pp 742-743.

(© 2008). Multiple Myeloma Disease Overview. Multiple Myeloma Research Foundation [On-line information]. PDF available for download at http://www.multiplemyeloma.org/downloads/about_myeloma/MMRF_Disease_Overview.pdf. Accessed August 2009.

(Modified 2009 July 23). General Information About Multiple Myeloma and Other Plasma Cell Neoplasms. National Cancer Institute. [On-line information]. Available online at http://www.cancer.gov/cancertopics/pdq/treatment/myeloma/patient/. Accessed August 2009.

(© 1995–2009). Overview: Beta-2 Microglobulin (B[2]-M), Urine. Mayo Clinic Mayo Medical Laboratories [On-line information]. Available online at http://www.mayomedicallaboratories.com/test-catalog/Overview/300243. Accessed August 2009.

(© 1995–2009). Overview: Beta-2-Microglobulin (Beta-2-M), Serum. Mayo Clinic Mayo Medical Laboratories [On-line information]. Available online at http://www.mayomedicallaboratories.com/test-catalog/Overview/9234. Accessed August 2009.

Seiter, K. and Shah, D. (Updated 2013 May 29). Multiple Myeloma. Medscape Reference [On-line information]. Available online at http://emedicine.medscape.com/article/204369-overview. Accessed June 2013.

(Modified 2013 May 17). Plasma Cell Neoplasms (Including Multiple Myeloma) Treatment (PDQ®). National Cancer Institute [On-line information]. Available online at http://www.cancer.gov/cancertopics/pdq/treatment/myeloma/patient/. Accessed June 2013.

Mayo Clinic staff (2011 August 16). Multiple myeloma. Mayo Clinic [On-line information]. Available online at http://www.mayoclinic.com/print/multiple-myeloma/DS00415/DSECTION=all&METHOD=print. Accessed June 2013.

(Revised 2013 February 12). Multiple Myeloma. American Cancer Society [On-line information]. Available online at http://www.cancer.org/cancer/multiplemyeloma/detailedguide/index. Accessed June 2013.

Durie, B. (2013). Patient Handbook: Multiple Myeloma. International Myeloma Foundation [On-line information]. Available online at http://myeloma.org/pdfs/Patient_Handbook_2013.pdf. Accessed June 2013.

(Revised 2012). Understanding Lab and Imaging Tests. Leukemia & Lymphoma Society [On-line information]. Available online through http://www.lls.org. Accessed June 2013.

(2011 December 7). Tumor Markers. National Cancer Institute [On-line information]. Available online at http://www.cancer.gov/cancertopics/factsheet/Detection/tumor-markers. Accessed June 2013.

Pagana, K. D. & Pagana, T. J. (© 2011). Mosby’s Diagnostic and Laboratory Test Reference 10th Edition: Mosby, Inc., Saint Louis, MO. Pp 680-682.

Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. Burtis CA, Ashwood ER, Bruns DE, eds. 4th edition, St. Louis: Elsevier Saunders; 2006, Pg 555.


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