Why is protein electrophoresis testing recommended?

Why Protein Electrophoresis Testing is Recommended

Protein electrophoresis (both serum and urine) is essential for detecting and quantifying monoclonal proteins (M-proteins) that indicate plasma cell proliferative disorders, including multiple myeloma, monoclonal gammopathy of undetermined significance (MGUS), and related malignancies. 1, 2

Primary Clinical Indications

Diagnostic Screening for Plasma Cell Disorders

• Serum protein electrophoresis (SPEP) should be performed whenever multiple myeloma, Waldenström's macroglobulinemia, primary amyloidosis, or related disorders are suspected. 3
• The test identifies M-proteins appearing as a homogeneous spike-like peak in the gamma or beta region, representing monoclonal immunoglobulin produced by malignant plasma cell clones. 2, 4
• SPEP is a core component of the minimal diagnostic workup recommended by the International Myeloma Working Group for all patients with suspected plasma cell disorders. 1

Evaluation of Specific Clinical Presentations

• Order SPEP when patients present with unexplained anemia, renal insufficiency, hypercalcemia, bone lesions (especially lytic lesions), or elevated total protein/globulin levels. 1, 5
• The test should be obtained during initial evaluation of radiolucent bone lesions of unknown etiology, though it has limitations (sensitivity 71%, specificity 83%) and should be combined with other tests. 6
• SPEP is indicated when investigating hyperviscosity syndrome symptoms or when rouleaux formation is noted on peripheral blood smear. 1, 5

Essential Testing Algorithm

Initial Screening Approach

• Both serum AND urine protein electrophoresis must be performed together—relying solely on serum testing misses 20% of patients who have secretory urinary proteins only. 2
• Agarose gel electrophoresis or capillary zone electrophoresis is preferred for screening. 1
• Immunofixation must follow any detected M-protein to confirm the type of heavy chain (IgG, IgA, IgM) and light chain (kappa or lambda). 1, 2

Complementary Quantification

• Measure M-protein by both densitometer tracing (from electrophoresis) AND nephelometric quantitation of immunoglobulins—these tests are complementary. 1
• Nephelometry is particularly useful for low levels of uninvolved immunoglobulins and for difficult-to-quantify immunoglobulins like IgA. 1, 2
• Serum free light chain assay should be added to detect light chain production and assess the kappa/lambda ratio. 1, 5

Urine Testing Requirements

• A 24-hour urine collection is obligatory—random urine samples are insufficient. 1, 2
• Urine protein electrophoresis (UPEP) detects Bence Jones proteins (free monoclonal light chains) that may be the only manifestation of disease. 2
• Immunofixation should be performed on concentrated 24-hour urine specimens even if no measurable protein or peak is visible on electrophoresis. 1

Monitoring and Surveillance Applications

Disease Monitoring

• All measurable parameters (heavy and light chains) should be systematically followed using the same test method for serial studies to ensure precise relative quantification. 2
• Monitor after each treatment cycle, then every two cycles once a response trend is observed, and less frequently once plateau is reached. 2
• SPEP quantifies disease burden and tracks treatment response in patients with established plasma cell disorders. 2

Risk Stratification

• For MGUS patients, repeat SPEP at 3-6 months after initial recognition to exclude multiple myeloma or Waldenström's macroglobulinemia. 1
• Low-risk MGUS (M-protein <15 g/L, IgG type, normal free light chain ratio) requires follow-up SPEP at 6 months, then every 2-3 years if stable. 1
• Intermediate/high-risk MGUS (M-protein >15 g/L, IgA or IgM type, abnormal FLC ratio) requires SPEP and complete blood count at 6 months, then annually for life. 1

Critical Pitfalls and Limitations

Technical Considerations

• Incomplete urine collection and inadequate concentration of urine samples lead to falsely negative results—ensure proper 24-hour collection technique. 2
• Immunofixation should not be neglected even when no visible peak is present to avoid false negatives. 2
• Nephelometric quantitation may overestimate monoclonal protein concentration when values are high. 1

Therapeutic Interference

• Daratumumab (anti-CD38 monoclonal antibody therapy) interferes with SPEP and immunofixation, potentially causing false positive results in patients with IgG kappa myeloma. 7
• Consider using FDA-approved daratumumab-specific IFE assays to distinguish therapeutic antibody from endogenous M-protein when assessing complete response. 7
• The disease can evolve into oligosecretory or light-chain-only forms, requiring serum free light chain monitoring in addition to SPEP. 2

Diagnostic Accuracy Limitations

• SPEP alone has insufficient positive predictive value (47%) for definitive diagnosis of myeloma in bone lesions—combine with urine electrophoresis, immunofixation, and free light chain assay, or obtain tissue biopsy. 6
• The test has high negative predictive value (94%), making it useful for ruling out plasma cell disorders. 6
• Mass spectrometry methods are emerging with superior sensitivity compared to gel-based electrophoresis, particularly for detecting minimal residual disease. 8, 9