In a patient with multiple myeloma, what does a B2 peak on serum protein electrophoresis (SPE) indicate?

Beta-2 Microglobulin in Multiple Myeloma

In multiple myeloma, a beta-2 (β2) peak on serum protein electrophoresis (SPEP) represents elevated beta-2 microglobulin levels, which is a critical prognostic marker that directly correlates with tumor burden and is used in staging and risk assessment of the disease. 1

Significance of Beta-2 Microglobulin in Multiple Myeloma

• Beta-2 microglobulin is a standard measure of tumor burden in multiple myeloma and is considered one of the most important prognostic parameters 1
• Elevated levels of beta-2 microglobulin reflect increased tumor mass and are associated with poorer outcomes 1
• The level of beta-2 microglobulin is incorporated into the International Staging System (ISS) for multiple myeloma, where it is combined with serum albumin to create a prognostic index 1

Diagnostic Context

• Beta-2 microglobulin measurement is part of the initial diagnostic workup recommended for all patients with suspected multiple myeloma 1
• This measurement should be performed alongside other critical tests including complete blood count, renal function tests, calcium levels, albumin, and lactate dehydrogenase (LDH) 1
• The combination of beta-2 microglobulin with serum albumin in the International Prognostic Index provides more comprehensive risk stratification than either marker alone 1

Clinical Implications

• Higher beta-2 microglobulin levels (>5.5 mg/L) are associated with advanced disease and poorer survival outcomes 1
• Serial measurements of beta-2 microglobulin can be used to monitor disease progression and response to treatment 2
• When interpreting beta-2 microglobulin levels, it's important to note that renal dysfunction can artificially elevate levels independent of tumor burden, as beta-2 microglobulin is cleared by the kidneys 1

Relationship to Other Laboratory Findings

• Beta-2 microglobulin should be interpreted in conjunction with other laboratory parameters including serum and urine protein electrophoresis, immunofixation, and serum free light chain assays 2, 3
• While monoclonal protein spikes typically appear in the gamma or beta region of SPEP, they can occasionally appear in other regions including the alpha-2 region 4
• The presence of beta-2 microglobulin elevation without a detectable M-protein may occur in nonsecretory myeloma, which represents approximately 3% of multiple myeloma cases 1

Management Implications

• The level of beta-2 microglobulin helps determine the appropriate treatment approach for patients with multiple myeloma 1
• Patients with higher beta-2 microglobulin levels may require more aggressive treatment strategies due to their higher risk disease 1
• Any abnormal findings on SPEP, including elevated beta-2 microglobulin, should prompt referral to a hematologist/oncologist for further evaluation and management 3

Common Pitfalls

• Misinterpreting elevated beta-2 microglobulin as solely indicative of renal dysfunction rather than considering it as a marker of tumor burden 1
• Failing to recognize that beta-2 microglobulin levels can be elevated in conditions other than multiple myeloma, including chronic inflammation, lymphoid malignancies, and renal insufficiency 5
• Not performing serial measurements of beta-2 microglobulin to monitor disease progression and response to treatment 2