Why we measure it

B2M has its most established clinical role as a prognostic marker in haematological malignancies — particularly multiple myeloma and non-Hodgkin's lymphoma. In multiple myeloma, serum B2M is a key component of the International Staging System (ISS): stage I myeloma is defined as B2M < 3.5 mg/L combined with albumin > 3.5 g/dL; stage III is B2M > 5.5 mg/L regardless of albumin. B2M elevation reflects the plasma cell burden and tumour mass, and is an independent predictor of survival. Multiple myeloma is most commonly diagnosed in adults over 65, but has a prolonged preclinical phase (monoclonal gammopathy of undetermined significance, MGUS) during which B2M may be gradually rising. Annual B2M in the autoimmune screen provides a marker for this slowly rising preclinical state — particularly when combined with a high ESR (another flag for paraproteinaemia). In non-Hodgkin's lymphoma, elevated B2M is associated with higher tumour burden and worse prognosis. B2M is not specific to malignancy — it is also elevated in active autoimmune disease and HIV — and must be interpreted alongside ESR, serum protein electrophoresis, and the clinical picture.

Why every 12 months

Annual testing as part of the Blueprint Bloodwork autoimmune and cancer surveillance panel. The slow-rising nature of B2M in MGUS progression means that annual measurement is sufficient to detect clinically meaningful changes before they become symptomatic.

What movement means

Standard upper reference limit for serum B2M is approximately 2.5 mg/L, though laboratory-specific ranges vary. Values should be interpreted in the context of renal function — B2M rises in proportion to declining GFR, so elevated B2M in the setting of impaired kidney function requires renal contextualisation before haematological workup.

In the protocol