Makindo Medical Notes

🔎 What is Beta-2 Microglobulin (B2M)?

• Beta-2 Microglobulin (B2M) is a low molecular weight protein (<12 kDa) found on the surface of all nucleated cells.
• It is the light chain component of MHC Class I molecules, essential for their stability and antigen presentation to CD8+ T cells.
• B2M is shed into the blood as cells turn over and is normally filtered by the glomeruli and reabsorbed in the proximal tubules.

🧬 Physiology

• Produced by all nucleated cells; levels reflect cellular turnover + immune activation.
• Maintains structural integrity of MHC-I, ensuring proper antigen presentation.
• Excreted almost entirely by the kidneys → sensitive to changes in renal function.

📖 Clinical Relevance

B2M is a useful biomarker for renal function, haematological malignancy prognosis, and immune activation.

📈 Causes of Elevated B2M

• Renal disease: CKD, AKI, tubular disorders → reduced clearance.
• Hematologic malignancies: Multiple Myeloma (part of ISS staging), lymphoma, leukaemia.
• Immune activation: Autoimmune (RA, SLE), chronic infection.
• HIV infection: Reflects ongoing immune activation; correlates with disease progression.
• Dialysis-related amyloidosis: Long-term dialysis → B2M amyloid deposits in joints/tendons.

🩺 Diagnostic & Prognostic Uses

• Renal function: Sensitive marker of tubular dysfunction; rises early in AKI.
• Oncology: Strong prognostic factor in Multiple Myeloma — higher B2M = worse survival (used in ISS staging).
• Immune monitoring: Tracks disease activity in HIV, autoimmune diseases, chronic infections.

📊 Normal vs Abnormal

• Normal range: ~1.0–2.5 mg/L (serum).
• High levels: >3 mg/L suggest pathology (renal impairment, immune activation, malignancy).

💡 Clinical Pearls

• In CKD, elevated B2M reflects reduced clearance rather than increased production.
• In multiple myeloma, both tumour burden and renal impairment elevate B2M → explains its prognostic power.
• Mnemonic (KIM-HIV): Kidney disease • Immune activation • Malignancy • HIV.

🌟 Summary

B2M is an MHC-I component and marker of cell turnover. It rises in renal failure, immune activation, and malignancy. It is especially important as a prognostic biomarker in multiple myeloma and in assessing immune system activity in chronic diseases.