What this test measures
Beta-2 microglobulin (β2M) is a small protein on the surface of all nucleated cells, forming part of the MHC class I molecule that presents antigens to the immune system. It is shed continuously into blood and cleared by the kidneys. Serum β2M concentration reflects both the rate of production (which rises in conditions with high cell turnover — lymphoma, multiple myeloma, chronic infection) and the rate of renal clearance (which falls in kidney failure).
The assay measures β2M in mg/L. Urine β2M is also measured in some kidney disorders — high urine β2M with normal serum suggests proximal tubular injury.
Why it matters
β2M has two main clinical roles. First, in haematology — multiple myeloma staging uses serum β2M as one of two components of the International Staging System (ISS): Stage I (β2M < 3.5 mg/L), Stage II (3.5–5.5), Stage III (> 5.5). Higher β2M means higher tumor burden and worse prognosis. β2M is also used to monitor response and assess relapse in myeloma, lymphoma, and chronic lymphocytic leukaemia (CLL).
Second, in kidney medicine — serum β2M rises with falling glomerular filtration rate, and urine β2M rises with proximal-tubule damage (cadmium poisoning, drug nephrotoxicity, Wilson disease, light-chain proximal tubulopathy). It is also used in HIV care as a non-specific marker of immune activation.
How to prepare
No fasting required. Inform the lab about any active infection (β2M is elevated transiently with infection and inflammation), pregnancy, and any kidney or haematological disease. Continue all medications. β2M is best interpreted alongside creatinine/eGFR to separate increased production from reduced renal clearance.
Markers & reference ranges
Reference ranges below are typical adult values. Your lab's reported range may differ slightly based on the assay platform and patient demographics — always read your report against the range printed on it.
| Marker | Normal range | If low | If high |
|---|---|---|---|
| Beta-2 Microglobulin (Serum) (mg/L)[1][2][3] | Adult 1.0 – 2.4 mg/L | < 1.0 mg/L: uncommon; usually not clinically meaningful. May occasionally reflect very low cell turnover. | > 2.4 mg/L with normal kidney function: increased production — multiple myeloma, lymphoma, CLL, chronic infection (HIV, hepatitis), autoimmune disease, acute viral illness. > 2.4 mg/L with raised creatinine: reduced renal clearance. ISS staging cut-offs for multiple myeloma: 3.5 and 5.5 mg/L. |
International Staging System (ISS) for Multiple Myeloma
| Stage | β2M (mg/L) | Albumin (g/dL) | Median survival (historical) |
|---|---|---|---|
| I | < 3.5 | ≥ 3.5 | 62 months |
| II | < 3.5 with low albumin, OR 3.5 – 5.5 | Any | 44 months |
| III | > 5.5 | Any | 29 months |
Frequently asked questions
Why is β2M used in multiple myeloma?
β2M reflects total tumor cell mass — the more myeloma cells, the more β2M is shed into blood. Combined with serum albumin, it forms the International Staging System (ISS), a simple and reproducible prognostic tool used worldwide.
Does high β2M always mean cancer?
No. β2M rises in kidney failure (reduced clearance), chronic infection (HIV, hepatitis), autoimmune disease (SLE, RA), and acute viral illness. The result has to be interpreted alongside creatinine and the clinical context.
Why is urine β2M sometimes measured?
Urine β2M is freely filtered by the glomerulus and reabsorbed by the proximal tubule. High urine β2M with normal glomerular filtration points to proximal tubule injury — cadmium or aristolochic acid exposure, drug nephrotoxicity (aminoglycosides, tenofovir), light-chain proximal tubulopathy, or Wilson disease.
Is β2M useful in lymphoma?
Yes — elevated β2M in non-Hodgkin lymphoma and CLL is associated with higher tumor burden and worse prognosis. It is part of several lymphoma prognostic indices.
Does HIV affect β2M?
Yes — β2M is elevated in HIV as a marker of immune activation. It was historically used as a surrogate for disease progression, now superseded by CD4 count and viral load.
How quickly does β2M respond to treatment?
In myeloma, β2M falls within weeks of effective treatment. Serial measurements are used together with serum free light chains and M-protein to track response and detect relapse early.
Will my report include a β2M-derived calculation?
Most labs report β2M alone. Multiple myeloma staging combining β2M with serum albumin (and LDH and FISH for revised ISS) is done by the treating haematologist using the lab values.
Related Immunology tests
Tests commonly ordered alongside BETA2 MICROGLOBULIN, or that help interpret an unexpected result.
Sources & references
- NCBI StatPearls — Beta-2 Microglobulin · accessed 2026-05-30T00:00:00.000Z
- NIH MedlinePlus — Beta-2 Microglobulin Test · accessed 2026-05-30T00:00:00.000Z
- Mayo Clinic Labs — Beta-2 Microglobulin, Serum · accessed 2026-05-30T00:00:00.000Z
- IMWG — International Staging System for Multiple Myeloma · accessed 2026-05-30T00:00:00.000Z
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