Clinical Indications for Serum Protein Electrophoresis
Serum protein electrophoresis (SPEP) should be ordered when you suspect plasma cell disorders, particularly multiple myeloma, monoclonal gammopathy of undetermined significance (MGUS), or AL amyloidosis, as well as for monitoring these conditions once diagnosed. 1
Primary Diagnostic Indications
Suspected Plasma Cell Disorders
SPEP is essential for initial investigation when clinical or laboratory findings suggest a plasma cell proliferative disorder 1:
- Unexplained anemia (normochromic, normocytic) 1
- Renal insufficiency without clear etiology 1
- Hypercalcemia (serum calcium ≥11.5 mg/dL) 1
- Bone lesions (lytic lesions, severe osteopenia, or pathologic fractures) 1
- Elevated total protein or globulin levels on routine chemistry 2
- Rouleaux formation on peripheral blood smear 1
- Back pain with concern for vertebral involvement 1
Specific Clinical Scenarios Requiring SPEP
When proteinuria is detected on routine urinalysis, both serum and 24-hour urine protein electrophoresis with immunofixation should be performed 1. This is critical because light chain disease may present with minimal or no serum M-protein 1.
For suspected AL amyloidosis, SPEP is mandatory as part of the initial workup, looking for evidence of an underlying plasma cell disorder 1.
In patients with peripheral neuropathy of unknown cause, SPEP helps identify paraprotein-associated neuropathies 2.
Monitoring Established Disease
Follow-up Testing
Once a monoclonal gammopathy is identified, SPEP serves different monitoring purposes based on risk stratification 1:
Low-risk MGUS (M-protein <15 g/L, IgG type, normal free light chain ratio): Repeat SPEP at 6 months after initial diagnosis to exclude progression, then every 2-3 years if stable 1
Intermediate/high-risk MGUS (M-protein ≥15 g/L, IgA or IgM type, or abnormal FLC ratio): SPEP at 6 months, then annually for life 1
Smoldering multiple myeloma: SPEP and complete blood count at 6 months, then annually 1
Active multiple myeloma: SPEP is used to quantify M-protein for assessing treatment response and detecting relapse 1
Technical Considerations and Pitfalls
SPEP should always be paired with immunofixation when a monoclonal protein is suspected or detected, as immunofixation confirms the presence and identifies the specific heavy and light chain type 1. SPEP alone may miss small M-proteins or light chain-only disease 1.
Nephelometric quantification of immunoglobulins should be performed alongside SPEP as these tests are complementary—nephelometry is particularly useful for detecting suppression of uninvolved immunoglobulins, which has prognostic significance 1.
Common pitfall: Ordering SPEP without urine studies. Both serum and 24-hour urine protein electrophoresis with immunofixation are required for complete evaluation, as approximately 20% of myeloma patients have light chain disease that may be missed by serum testing alone 1.
When SPEP is NOT the Primary Test
For chronic inflammatory conditions, liver disease, or nephrotic syndrome, SPEP may show characteristic patterns (polyclonal gammopathy, beta-gamma bridging, hypoalbuminemia) but is typically ordered to characterize abnormal total protein or globulin levels rather than as a primary diagnostic tool 3, 2.
SPEP has limited utility as a general screening test in asymptomatic patients without specific risk factors for plasma cell disorders 4. The test performs best when clinical suspicion is present based on the findings listed above 4.