B2-Microglobulin

What is β₂-Microglobulin?

β₂-Microglobulin (B2M) is a low–molecular-weight protein (~11.8 kDa) that forms the light chain of MHC Class I molecules present on all nucleated cells.

Constantly shed into blood

Freely filtered by glomeruli

Almost completely reabsorbed and catabolized in proximal tubules

Normal Reference Range

• Serum: ~0.7–1.8 mg/L
• Urine: < 300 µg/day
  (Ranges vary slightly by lab)

1️⃣ Marker of Renal Function

A. Glomerular Dysfunction

↑ Serum B2M occurs when:

• Reduced GFR
• Chronic kidney disease (CKD)
• Acute kidney injury

Because it is filtered by the kidney, impaired filtration increases blood levels.

B. Tubular Dysfunction

↑ Urinary B2M occurs in:

• Proximal tubular damage
• Drug-induced nephrotoxicity
• Heavy metal toxicity
• Tubulointerstitial nephritis

Since it is normally reabsorbed in proximal tubules, tubular injury increases urinary excretion.

2️⃣ Hematological Malignancies

Serum B2M is an important tumor marker and prognostic indicator in:

• Multiple Myeloma
• Chronic Lymphocytic Leukemia
• Non-Hodgkin Lymphoma

Clinical importance:

• Reflects tumor burden
• Used in staging and prognosis
• Higher levels → poorer prognosis

In Multiple Myeloma, it is part of the International Staging System (ISS).

3️⃣ Inflammatory & Autoimmune Disorders

Levels may increase in:

• Rheumatoid arthritis
• Systemic lupus erythematosus
• Chronic infections (e.g., HIV)

Reason:

• Increased cell turnover
• Immune activation

4️⃣ Dialysis-Related Amyloidosis

Long-term dialysis patients may develop:

• β₂-microglobulin amyloid deposition
• Joint pain and carpal tunnel syndrome

Occurs due to inadequate clearance during dialysis.