Beta-2 Microglobulin: Multiple Myeloma Staging
Content last reviewed 2026-09-12 · Educational information — not medical advice
Quick answer
Beta-2 microglobulin (B2M) is a cell-surface protein elevated in B-cell cancers (myeloma, lymphoma, CLL) and kidney failure. Its primary modern use: ISS staging for multiple myeloma — alongside albumin — where B2M >5.5 mg/L defines Stage III disease.
Biology and elimination
B2M sheds from all nucleated cells — constant low-level presence (~1–2 mg/L normally). Eliminated by glomerular filtration, so kidney impairment raises it independently of cancer — the major interpretation confound. Myeloma cells overexpress it proportionally to disease burden.
Multiple myeloma staging
International Staging System (ISS): Stage I: B2M <3.5 + albumin ≥3.5 · Stage II: neither I nor III · Stage III: B2M ≥5.5. Combined with LDH and cytogenetics (R-ISS) for refined prognostication. B2M also tracks treatment response and recurrence.
Non-myeloma elevations
Any B-cell malignancy (lymphoma, CLL), HIV infection, autoimmune disease, inflammatory conditions, and — critically — ANY cause of kidney impairment. Always pair with creatinine/eGFR before attributing B2M elevation to malignancy alone.
Monitoring applications
CLL prognosis (Rai/Binet staging incorporate B2M), lymphoma treatment monitoring, and selected autoimmune/inflammatory activity tracking. Renal-transplant recipients use B2M trends for rejection surveillance in some protocols.
Frequently asked questions
B2M 3.0 with creatinine 2.0 — myeloma or kidney?
Kidney-disease elevation likely — B2M rarely normalizes with clean eGFR. Renal-function-adjusted interpretation needed.
Do I need fasting?
No — B2M unaffected by meals; timing and posture (standing vs lying) cause minimal variation.