Lab result explainedInflammationLast updated November 11, 2026

Beta-2 microglobulin (B2M) test: normal range, what a high level means, and myeloma staging cut-offs

Beta-2 microglobulin (B2M) · Beta-2 microglobulin, serum (also measured in urine and cerebrospinal fluid); usually ordered with albumin, LDH, creatinine and SPEP · reported in mg/L in serum (numerically the same as µg/mL); µg/L or mg/L in urine, sometimes indexed to creatinine (µg/g creatinine)

Beta-2 microglobulin (B2M) is a small protein found on the surface of nearly every cell in the body, where it forms part of the structure that displays protein fragments to the immune system. Cells shed it continuously into the blood, the kidneys filter it out and break it down, and the balance between those two processes keeps the serum level at about 0.8 to 2.2 mg/L in healthy adults. A B2M blood test is used for two different purposes: to stage and follow blood cancers such as multiple myeloma, lymphoma and chronic lymphocytic leukemia, in which rapidly dividing white cells shed more of it, and to assess kidney function, because the level climbs as filtration falls.

In multiple myeloma, B2M is one of the two laboratory values in the International Staging System (ISS): a level under 3.5 mg/L with a normal albumin is stage I, a level of 5.5 mg/L or more is stage III, and everything in between is stage II. In the original ISS study, median survival was 62 months for stage I, 44 months for stage II and 29 months for stage III, figures that have improved considerably with modern treatment but that still reflect the ranking. The revised ISS (R-ISS) adds LDH and high-risk chromosome abnormalities. B2M is also part of the prognostic index for chronic lymphocytic leukemia (above 3.5 mg/L is an adverse factor) and of several lymphoma indices.

Because the kidneys remove B2M, any fall in kidney function raises the blood level, and in people on long-term dialysis it accumulates to 20 to 50 mg/L and can deposit in joints and tendons as dialysis-related amyloidosis. The test is therefore never read without a creatinine or eGFR alongside it, and a high B2M in someone with kidney disease and no blood-cancer features usually reflects the kidneys rather than a tumor. Urine B2M is a separate test that detects damage to the kidney tubules, which normally reabsorb almost all of the filtered protein.

B2M at a glance

  • What it is: a small protein shed from the surface of all nucleated cells; it rises when cell turnover increases (blood cancers, infection, inflammation) or when the kidneys clear it less well.
  • Normal serum level: about 0.8–2.2 mg/L in adults (some labs quote up to 2.4 or 2.7 mg/L); urine under about 300 µg/L (0.3 mg/L). Labs differ.
  • Myeloma staging: ISS stage I is B2M under 3.5 mg/L with albumin 3.5 g/dL or more; stage III is B2M 5.5 mg/L or more; stage II is everything else.
  • A high serum level without a blood cancer most often means reduced kidney function; people on dialysis commonly run 20–50 mg/L.
  • A high urine level means the kidney tubules are leaking it: tubular injury from drugs, heavy metals, interstitial nephritis or transplant rejection.
  • It is not a screening test for cancer and a low level needs no action; next step for an unexplained high value is creatinine or eGFR, a CBC, SPEP with free light chains, and LDH.

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What B2M measures

B2M is the light chain of the MHC class I complex, the structure that every nucleated cell uses to present fragments of its internal proteins to T cells. It is a single protein of 11,800 daltons, bound non-covalently to the heavy chain, and it detaches and enters the blood as cells turn over. Production is highest in lymphocytes, which is why lymphoid cancers, viral infections such as HIV, cytomegalovirus and hepatitis, and autoimmune diseases that activate lymphocytes all raise it. Rate of production in a healthy adult is fairly constant at around 2 to 4 mg per kilogram per day.

Because it is so small, B2M passes freely through the glomerular filter, and more than 99.9 percent of what is filtered is then reabsorbed and broken down by the cells of the proximal tubule. Only a tiny amount reaches the urine. This makes serum B2M behave like creatinine or cystatin C as an index of filtration (it has been built into research eGFR equations alongside cystatin C) and makes urine B2M a sensitive index of tubular health: when tubular cells are injured by aminoglycoside antibiotics, cisplatin, tenofovir, cadmium, lead, mercury or interstitial nephritis, reabsorption fails and urine B2M climbs well before creatinine changes.

The serum assay is an immunoassay (immunoturbidimetric or chemiluminescent) reported in mg/L; some labs use µg/mL, which is numerically identical. Fasting is not needed. Levels rise modestly with age and are slightly higher in people with active inflammation, so the figure is interpreted with CRP, kidney function and the clinical picture. Urine B2M breaks down quickly in acidic urine, so the sample must be processed promptly and sometimes alkalinized; a first-morning sample is usually requested.

Normal range for B2M

Reference ranges vary between labs and by age, sex and pregnancy. Use the range printed on your own report.

GroupTypical range (mg/L in serum (numerically the same as µg/mL); µg/L or mg/L in urine, sometimes indexed to creatinine (µg/g creatinine))Notes
Adult serum, normalAbout 0.8–2.2 mg/LUpper limits of 2.4 to 2.7 mg/L are used by some laboratories; levels drift upward with age. Use the printed range.
Urine, normalBelow about 300 µg/L (0.3 mg/L), or below about 160 µg/g creatinineHigher values indicate proximal tubular dysfunction. Fresh, promptly processed sample needed.
Myeloma ISS stage IB2M below 3.5 mg/L and serum albumin 3.5 g/dL or higherBest prognostic group. R-ISS stage I additionally requires normal LDH and no high-risk FISH abnormalities.
Myeloma ISS stage IINeither stage I nor stage III (B2M below 3.5 with albumin under 3.5, or B2M 3.5–5.4 mg/L)Intermediate group.
Myeloma ISS stage IIIB2M 5.5 mg/L or higherHighest-risk group; values partly reflect kidney involvement by myeloma.
Chronic lymphocytic leukemiaAbove 3.5 mg/L is an adverse factor in the CLL-IPIScored alongside age, stage, IGHV mutation status and TP53.
Reduced kidney function (not on dialysis)Roughly 3–10 mg/L, rising as eGFR fallsInterpret with eGFR; a level in this band is expected with CKD stage 3 to 5 and does not by itself suggest cancer.
Long-term hemodialysisTypically 20–50 mg/LDialysis-related amyloidosis develops after about 5 to 10 years at these levels; high-flux dialyzers remove more B2M.

High beta-2 microglobulin

A high serum B2M means either that cells are shedding more of it, that the kidneys are clearing less of it, or both. The first question is always kidney function. If eGFR is reduced, a B2M of 3 to 10 mg/L is largely explained by the kidneys, and the value is used for little more than tracking. If kidney function is normal, a persistently raised B2M points to increased cell turnover: a lymphoid cancer (myeloma, lymphoma, chronic lymphocytic leukemia, Waldenström macroglobulinemia), a chronic viral infection (HIV, hepatitis B or C, cytomegalovirus, Epstein-Barr virus), or an active autoimmune or inflammatory disease (lupus, rheumatoid arthritis, Sjögren's syndrome, Crohn's disease, sarcoidosis).

In someone with a known plasma-cell or lymphoid cancer, B2M is a measure of tumor burden and biological activity. In myeloma the ISS cut-offs of 3.5 and 5.5 mg/L separate three groups with distinctly different outlooks, and B2M also falls with effective treatment and rises again at relapse, which is why it is repeated through the course of treatment. In lymphoma, a B2M above the laboratory's upper limit is an adverse factor in the follicular lymphoma index (FLIPI2), the mantle cell index (MIPI-b) and several Hodgkin and diffuse large B-cell series; in CLL, a level above 3.5 mg/L contributes to the CLL-IPI. None of these uses make B2M a diagnostic test; it refines the prognosis once the disease is diagnosed by biopsy or marrow examination.

B2M is not a cancer screening test. It is raised in many benign conditions, it is normal in a proportion of early cancers, and no cancer is diagnosed from it alone. An isolated high value with normal kidney function, normal blood counts, a normal SPEP and no symptoms is usually repeated in a few weeks after excluding infection and inflammation. A high urine B2M has a different meaning entirely: it indicates proximal tubular injury, from drugs, heavy metals, interstitial nephritis, Fanconi syndrome, light-chain kidney disease or rejection of a kidney transplant, and it can precede any change in creatinine.

Common causes

  1. Reduced kidney function (chronic kidney disease, acute kidney injury)

    The most common cause overall. Because B2M is cleared almost entirely by glomerular filtration, serum levels rise in step with falling eGFR, reaching 3 to 10 mg/L in moderate to severe CKD and 20 to 50 mg/L on dialysis. Serum B2M tracks GFR about as well as cystatin C and is less affected by muscle mass than creatinine.

  2. Multiple myeloma and other plasma-cell disorders

    Malignant plasma cells shed B2M, and myeloma also damages the kidneys, so levels reflect both tumor burden and renal involvement. Used for ISS and R-ISS staging (3.5 and 5.5 mg/L) and for monitoring response and relapse. Mildly raised in some people with MGUS and smoldering myeloma.

  3. Lymphoma and chronic lymphocytic leukemia

    Non-Hodgkin lymphoma, Hodgkin lymphoma, CLL and Waldenström macroglobulinemia raise B2M in proportion to disease bulk and proliferation. Above 3.5 mg/L is an adverse factor in the CLL-IPI; above the upper limit of normal counts in FLIPI2 and MIPI-b.

  4. HIV and other chronic viral infections

    Activated lymphocytes shed B2M, so untreated HIV, hepatitis B and C, cytomegalovirus and Epstein-Barr virus all raise it; in HIV the level falls on effective antiretroviral therapy. Before viral load testing, B2M was used to track HIV progression.

  5. Autoimmune and inflammatory disease

    Systemic lupus, rheumatoid arthritis, Sjögren's syndrome, Crohn's disease, sarcoidosis and vasculitis raise B2M during active disease, usually to 2.5 to 5 mg/L, alongside CRP and ESR; the level falls with control of the disease.

  6. Long-term dialysis and dialysis-related amyloidosis

    Conventional dialysis removes B2M poorly, so it accumulates over years and polymerizes into amyloid fibrils in tendons, joints and bones, causing carpal tunnel syndrome, shoulder pain, bone cysts and fractures. Higher serum B2M predicted higher mortality in the HEMO study (about 11 percent higher per 10 mg/L).

  7. Solid tumors and other cancers

    Some kidney, lung, breast and gastrointestinal cancers, and leukemias, raise B2M modestly, usually with other findings. B2M is not used to screen for or diagnose solid tumors.

  8. Older age, inflammation of any kind and recent infection

    Levels rise gradually with age and transiently with any significant infection or inflammatory illness, which is why an unexplained mildly raised value is repeated once you are well.

  9. Proximal tubular injury (high urine B2M)

    Aminoglycosides, cisplatin, tenofovir, lithium, cadmium, lead and mercury exposure, acute interstitial nephritis (often from NSAIDs, proton pump inhibitors or antibiotics), Fanconi syndrome, myeloma light chains and kidney transplant rejection all impair reabsorption, raising urine B2M before serum creatinine moves.

Symptoms that can go with it

  • Often none; the level is usually found during staging or kidney assessment rather than because of symptoms
  • Fatigue, pallor and breathlessness from anemia in myeloma, lymphoma or kidney disease
  • Bone pain, fractures, thirst or confusion (high calcium) in myeloma
  • Painless swollen lymph nodes, night sweats, fevers and weight loss in lymphoma or CLL
  • Swollen legs, foamy urine, reduced urine output or itching in kidney disease
  • Wrist numbness (carpal tunnel), shoulder pain and stiff joints in long-term dialysis patients with amyloid deposits
  • Recurrent infections or symptoms of an underlying autoimmune or viral illness

Low beta-2 microglobulin

A low or low-normal B2M has no recognized clinical significance in adults and does not need investigation. It simply indicates normal kidney clearance and no excess cell turnover, which is the expected state in a healthy person. In someone being treated for myeloma, lymphoma or CLL, a fall in B2M toward the normal range is a favorable sign that treatment is reducing the tumor burden, and in a person with HIV it tracks suppression of the virus.

Values below the quoted range are occasionally reported and usually reflect laboratory variation, dilution of a sample or, rarely, a genetic variant affecting the protein. There is no deficiency syndrome of B2M diagnosed by this blood test; the only known human deficiency is an extremely rare inherited immunodeficiency identified by other means.

Common causes

  1. Normal health

    Good kidney function and a low rate of lymphocyte turnover keep serum B2M in the lower half of the range; younger adults typically run 1 to 1.6 mg/L.

  2. Response to treatment

    Effective chemotherapy or immunotherapy for myeloma, lymphoma or CLL, and effective antiretroviral therapy in HIV, lower B2M, often into the normal range; a renewed rise suggests relapse.

  3. Hemodilution or sample handling

    A sample drawn immediately after intravenous fluids, or diluted during processing, reads low. Urine B2M also degrades in acidic urine left standing, giving a falsely low urine result.

  4. High-flux hemodialysis or hemodiafiltration

    In dialysis patients, a lower B2M than expected reflects better clearance by high-flux membranes or convective techniques, which is a treatment goal.

Symptoms that can go with it

  • None; a low B2M does not cause symptoms
  • If a low result conflicts with other findings (for example, a known active lymphoma), the sample is simply repeated

Read it alongside

  • Creatinine and eGFR — essential; a high B2M is interpreted completely differently when the kidneys are impaired.
  • Albumin — the other half of the ISS; stage I requires albumin of 3.5 g/dL or more as well as B2M under 3.5 mg/L.
  • LDH — added to B2M and albumin in the revised ISS (R-ISS) and raised with high tumor turnover in lymphoma and myeloma.
  • SPEP, immunofixation and free light chains — identify the plasma-cell clone that a high B2M may reflect.
  • Complete blood count and lymphocyte count — anemia, thrombocytopenia or a high lymphocyte count points toward the marrow or lymphoid cause.
  • Calcium — above 11 mg/dL is a myeloma-defining feature.
  • CRP and ESR — help decide whether a modest rise is inflammatory rather than malignant.
  • Cystatin C — another small protein cleared by filtration; concordant results confirm a kidney explanation.
  • Urine albumin/creatinine ratio and urine protein — urine B2M flags tubular damage; albuminuria flags glomerular damage, and the two together localize the injury.

What usually happens next

  1. If B2M is high and eGFR is reduced, the kidney explanation usually suffices; the next step is routine CKD assessment (urine albumin, blood pressure, glucose, imaging as needed) rather than a cancer work-up, unless blood counts, calcium or protein studies are also abnormal.
  2. If B2M is high with normal kidney function, expect a CBC with differential, CRP, SPEP with immunofixation and free light chains, LDH, and tests for HIV and hepatitis where appropriate; a persistently raised value with abnormal counts or a paraprotein leads to hematology referral.
  3. If you have myeloma, ask which ISS or R-ISS stage your B2M and albumin place you in, and expect B2M to be repeated at each response assessment; a fall of more than half with treatment is typical of a good response.
  4. If you have lymphoma or CLL, B2M feeds into the prognostic index your hematologist uses (FLIPI2, MIPI-b, CLL-IPI); it does not by itself decide whether to treat.
  5. A high urine B2M prompts a review of medications (aminoglycosides, tenofovir, cisplatin, lithium, NSAIDs, proton pump inhibitors), occupational or environmental metal exposure, and, in transplant recipients, assessment for rejection.
  6. A mildly raised result with no explanation is repeated in 4 to 8 weeks once any infection or flare has settled; a single value is rarely acted on.

Diet, lifestyle and natural levers with evidence

What can move B2M once the cause is known. Nothing here replaces finding the cause.

No supplement or diet lowers B2M directly; the number follows the kidneys and the underlying disease

Strong evidence

B2M is a marker, not a target: it falls when the condition driving it is treated (chemotherapy for myeloma or lymphoma, antiretroviral therapy for HIV, control of an autoimmune flare) and rises with loss of kidney function. No herb, vitamin or dietary pattern has been shown in trials to lower serum B2M independently of those causes. Timing matters: a value drawn during an infection, a flare or an episode of dehydration will be higher, so a borderline result is repeated when you are well and hydrated.

Protecting kidney function: blood pressure, glucose, hydration and avoiding nephrotoxins

Strong evidence

Because serum B2M rises in step with falling eGFR, the measures that slow CKD progression are the measures that keep B2M down: blood pressure control (trials such as SPRINT and the KDIGO targets show slower eGFR decline with systolic pressure under 130 mmHg), glucose control in diabetes, limiting sodium to under 2 g a day, and avoiding regular NSAIDs, which raise the risk of acute kidney injury and interstitial nephritis. In the HEMO trial of 1,813 dialysis patients, each 10 mg/L higher B2M was associated with about 11 percent higher mortality, which is why nephrologists favor high-flux dialysis that clears it better.

Fluid and potassium targets differ in advanced kidney disease and heart failure; follow your nephrologist's advice rather than general hydration guidance.

Reducing cadmium exposure, chiefly by not smoking

Moderate evidence

Cadmium accumulates in the proximal tubule and is a classic cause of a raised urine B2M. Tobacco smoke is the main non-occupational cadmium source: smokers have roughly twice the blood cadmium of non-smokers, and population studies (including US NHANES analyses) link higher cadmium burden to tubular proteinuria and faster kidney function decline. Stopping smoking halts further accumulation; occupational exposure in battery, pigment, plating and welding work warrants workplace monitoring.

Physical activity and healthy weight

Preliminary evidence

Serum B2M rises with age and is higher in people with obesity, inactivity and metabolic syndrome in cross-sectional studies, where it behaves as a general marker of inflammation and cardiovascular risk independent of eGFR. Small intervention studies report modest falls in B2M with weight loss and aerobic training, but the data are limited and the effect is far smaller than that of kidney function or disease activity. Activity and weight are worth addressing for their own sake rather than to move this number.

When to see a clinician promptly

  • A sharp fall in urine output, rapidly rising creatinine, or swelling and breathlessness in someone with a known plasma-cell disorder: possible light-chain kidney injury, which is reversible only if treated within days.
  • Severe back pain with leg weakness or numbness, or loss of bladder or bowel control, in anyone with myeloma or lymphoma: possible spinal cord compression, an emergency.
  • Confusion, severe thirst, vomiting or drowsiness, which can indicate dangerously high calcium in myeloma.
  • Fever over 100.4 F (38 C) during treatment for myeloma, lymphoma or CLL, when the immune system is suppressed.
  • Rapidly enlarging lymph nodes, drenching night sweats, unexplained weight loss of more than 10 percent, or a new high B2M with abnormal blood counts.
  • New wrist numbness, shoulder pain or a bone fracture in someone on long-term dialysis, which may indicate dialysis-related amyloidosis.

Frequently asked questions

What is the normal range for beta-2 microglobulin?

In blood, about 0.8 to 2.2 mg/L in healthy adults, with some laboratories quoting an upper limit of 2.4 or 2.7 mg/L; levels rise slightly with age. In urine, under about 300 µg/L (0.3 mg/L). Some reports use µg/mL, which gives the same numbers as mg/L. Always compare with the range printed on your own report, and remember that any reduction in kidney function raises the blood level.

What does a high beta-2 microglobulin mean?

Either the kidneys are clearing less of it or cells are shedding more. With reduced kidney function, a level of 3 to 10 mg/L is expected and usually needs no further explanation. With normal kidneys, a persistently high level points to increased lymphocyte or plasma-cell turnover: myeloma, lymphoma, chronic lymphocytic leukemia, a chronic viral infection such as HIV or hepatitis, or an active autoimmune disease. A single mildly raised value during an infection is repeated when you are well.

How is beta-2 microglobulin used to stage myeloma?

The International Staging System uses B2M and albumin. Stage I is B2M under 3.5 mg/L with albumin 3.5 g/dL or more; stage III is B2M of 5.5 mg/L or more; stage II is everything in between. The revised ISS adds LDH and high-risk chromosomal abnormalities (del17p, t(4;14), t(14;16)) to refine the groups. Staging is done at diagnosis; B2M is then repeated to track response and relapse.

Can kidney disease alone raise beta-2 microglobulin?

Yes, and it is the most common reason for a high result. B2M is filtered by the glomerulus and broken down by the tubules, so as eGFR falls the blood level climbs; people with moderate CKD often run 3 to 6 mg/L and dialysis patients 20 to 50 mg/L. This is why B2M is never read without a creatinine or eGFR, and why a high value in someone with kidney disease and normal blood counts and protein studies is not taken as a sign of cancer.

Is beta-2 microglobulin a cancer marker?

It is used as a tumor marker for prognosis and monitoring in blood cancers that are already diagnosed, mainly myeloma, lymphoma and CLL, but it is not a screening or diagnostic test for cancer. It is raised in kidney disease, infections, inflammation and autoimmune conditions, and can be normal in early cancer. A high B2M alone never establishes a cancer diagnosis; that requires blood counts, protein studies, imaging and usually a biopsy or bone marrow examination.

What does beta-2 microglobulin in urine mean?

The kidney tubules normally reabsorb more than 99.9 percent of filtered B2M, so a high urine level means the proximal tubules are injured. Common causes are drugs (aminoglycoside antibiotics, cisplatin, tenofovir, lithium), heavy-metal exposure (cadmium, lead, mercury), acute interstitial nephritis, Fanconi syndrome, myeloma light chains and rejection of a transplanted kidney. It can rise before creatinine changes. The sample must be fresh, because B2M breaks down in acidic urine that is left standing.

What is dialysis-related amyloidosis?

In people on dialysis for many years, B2M that the treatment cannot remove builds up to 20 to 50 mg/L in the blood and slowly forms amyloid deposits in tendons, joint linings and bone, typically after 5 to 10 years. The usual results are carpal tunnel syndrome, chronic shoulder pain, trigger fingers, bone cysts and sometimes fractures or spinal problems. Modern high-flux dialyzers and hemodiafiltration remove more B2M and have made it less common; kidney transplantation stops the process.

Does beta-2 microglobulin go down with treatment?

Yes. In myeloma, lymphoma and CLL, B2M falls as the tumor burden falls and is often back in the normal range at remission; a rise during follow-up is one of the early signals of relapse. In HIV it falls within months of effective antiretroviral therapy, and in autoimmune disease it falls as the flare is controlled. In kidney disease it only falls if kidney function improves or dialysis clearance increases.

References

  1. Beta 2 microglobulin (B2M) tumor marker test. MedlinePlus, US National Library of Medicine (2023)View source
  2. Greipp PR, San Miguel J, Durie BG, et al.. International staging system for multiple myeloma. Journal of Clinical Oncology (2005)
  3. Palumbo A, Avet-Loiseau H, Oliva S, et al.. Revised International Staging System for multiple myeloma: a report from International Myeloma Working Group. Journal of Clinical Oncology (2015)
  4. International CLL-IPI working group. An international prognostic index for patients with chronic lymphocytic leukaemia (CLL-IPI): a meta-analysis of individual patient data. Lancet Oncology (2016)
  5. Cheung AK, Rocco MV, Yan G, et al.. Serum beta-2 microglobulin levels predict mortality in dialysis patients: results of the HEMO study. Journal of the American Society of Nephrology (2006)
  6. Inker LA, Tighiouart H, Coresh J, et al.. GFR estimation using β-trace protein and β2-microglobulin in CKD. American Journal of Kidney Diseases (2016)
  7. Argyropoulos CP, Chen SS, Ng YH, et al.. Rediscovering beta-2 microglobulin as a biomarker across the spectrum of kidney diseases. Frontiers in Medicine (2017)
  8. Gejyo F, Yamada T, Odani S, et al.. A new form of amyloid protein associated with chronic hemodialysis was identified as β2-microglobulin. Biochemical and Biophysical Research Communications (1985)
  9. Tumor markers. National Cancer Institute (2024)View source
  10. Federico M, Bellei M, Marcheselli L, et al.. Follicular lymphoma international prognostic index 2: a new prognostic index for follicular lymphoma developed by the International Follicular Lymphoma Prognostic Factor Project. Journal of Clinical Oncology (2009)
  11. Multiple myeloma. Merck Manual Professional Version (2024)
  12. Järup L, Åkesson A. Cadmium exposure and nephropathy. Toxicology and Applied Pharmacology (2009)

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This page is educational and is not medical advice or a diagnosis. Lab results have to be interpreted together with your history, symptoms and other results by a clinician who knows you. Do not start or stop a supplement to change a lab value before the cause is known.