What laboratory workup should be performed for an elevated serum protein electrophoresis?

Laboratory Workup for Elevated Serum Protein Electrophoresis

When serum protein electrophoresis reveals an abnormality, immediately order serum immunofixation, complete blood count with differential, comprehensive metabolic panel (including calcium and creatinine), quantitative immunoglobulins by nephelometry, and 24-hour urine protein electrophoresis with immunofixation. 1, 2

Essential Initial Testing Panel

The International Myeloma Workshop Consensus Panel established the following mandatory workup 1:

Blood Tests

• Serum immunofixation electrophoresis – Confirms the presence of monoclonal protein and definitively identifies the heavy-chain type (IgG, IgA, IgM) and light-chain type (kappa or lambda) 1, 2
• Complete blood count with differential and peripheral blood smear – Evaluate for anemia (hemoglobin <10 g/dL or ≥2 g/dL below normal), rouleaux formation, and circulating plasma cells 1
• Comprehensive metabolic panel – Must include:
  • Serum calcium (hypercalcemia defined as ≥11.5 mg/dL) 1, 2
  • Serum creatinine (renal insufficiency defined as ≥2 mg/dL) 1, 2
  • Liver function tests and electrolytes 1
  • Albumin level 1
• Quantitative immunoglobulins (IgG, IgA, IgM) by nephelometry – Provides baseline levels and helps classify the gammopathy type; this is complementary to densitometer tracing of the M-protein 1, 2
• Serum free light chain assay with kappa/lambda ratio – An abnormal ratio (<0.125 or >8) is an independent risk factor for progression with hazard ratio of 3.5 2, 3
• Beta-2 microglobulin and lactate dehydrogenase – Reflects tumor burden and provides independent prognostic information 1, 3

Urine Tests

• 24-hour urine collection for protein electrophoresis and immunofixation – This is mandatory because approximately 20% of plasma cell disorders secrete monoclonal proteins only in urine, and serum testing alone will miss these cases 1, 2
• Routine urinalysis – Screen for proteinuria 1
• Random urine samples are insufficient and cannot replace 24-hour collections for accurate quantification 1, 2

Bone Marrow Evaluation

• Unilateral bone marrow aspirate and/or biopsy – Required to confirm ≥10% clonal plasma cells for diagnosis of multiple myeloma 1
• CD138 immunostaining – Should be used whenever possible to accurately determine plasma cell percentage 1
• Cytogenetics (metaphase karyotype and FISH) – Identifies high-risk features such as del(17p), t(4;14), and t(14;16) 1, 3

Imaging Studies

• Skeletal bone survey – Including spine, pelvis, skull, humeri, and femurs to detect lytic lesions, severe osteopenia, or pathologic fractures 1
• MRI in certain circumstances – When indicated by clinical presentation 1

Critical Technical Considerations

Measure M-protein by both densitometer tracing and nephelometric quantitation because these methods are complementary 1, 2. However, be aware that nephelometric quantitation may overestimate monoclonal protein concentration when values are high 1, 2, 3.

Immunofixation must follow any detected M-protein to definitively identify its composition 2, 4, 5. Immunofixation has greater sensitivity than electrophoresis alone and can detect small or light chain bands not apparent on standard electrophoresis, including biclonal disease 5, 6.

In patients with hypogammaglobulinemia and apparently normal SPEP, immunofixation can still reveal an M-protein in approximately 10% of cases, particularly when the alpha2-globulin/alpha1-globulin ratio is elevated, hemoglobin is low, or creatinine is elevated 6.

Follow-Up Monitoring Strategy

After initial detection of a monoclonal protein 2:

If MGUS (Monoclonal Gammopathy of Undetermined Significance)

• Repeat SPEP at 3-6 months to exclude evolution to multiple myeloma or Waldenström's macroglobulinemia 2
• Low-risk MGUS (M-protein <15 g/L, IgG type, normal free light chain ratio): SPEP at 6 months, then every 2-3 years if stable 2
• Intermediate/high-risk MGUS (M-protein ≥15 g/L, IgA or IgM type, or abnormal free light chain ratio): SPEP at 6 months, then annually for life, plus baseline bone marrow biopsy 2

If Smoldering Multiple Myeloma

• Initial repeat at 2-3 months, then every 4-6 months during the first year, then every 6-12 months thereafter 2

For Active Disease Monitoring

• All measurable parameters must be followed, including both light and heavy chain analysis 1, 2
• Use the same analytical method for serial measurements to ensure accurate comparison over time 2
• Response assessment after one cycle of therapy, then every other cycle once a response trend is observed 1

Common Pitfalls to Avoid

Never rely on serum testing alone – 20% of cases will be missed without concurrent urine studies 1, 2.

Incomplete or inadequately concentrated urine collections lead to falsely negative results; proper 24-hour collection technique is essential 1, 2.

Do not perform routine screening in asymptomatic individuals without risk factors; MGUS prevalence is only ~3.2% in persons >50 years, and most never progress 2.