Should serum immunofixation electrophoresis be ordered to confirm a monoclonal protein on serum protein electrophoresis?

Yes, order serum immunofixation electrophoresis

Serum immunofixation electrophoresis (IFE) should be ordered to confirm and characterize any monoclonal protein detected on serum protein electrophoresis (SPEP), as it is the reference standard for definitive identification and typing of monoclonal gammopathies 1.

Why IFE is Essential

The most recent EHA-EMN guidelines (2025) and established International Myeloma Workshop consensus recommendations consistently identify serum IFE as a core component of the standard investigative workup for suspected plasma cell disorders 2, 1. Here's the algorithmic approach:

When to Order IFE:

1. Any abnormal SPEP profile - particularly when a monoclonal peak is detected 1
2. Even with normal SPEP - if clinical suspicion for multiple myeloma or related disorders remains high 3, 4
3. Hypogammaglobulinemia - where small monoclonal components may be masked by reduced γ-globulin levels 5
4. β-region abnormalities - where monoclonal proteins can be cloaked by normal constituents 6

Superior Diagnostic Performance:

Recent data (2025) demonstrates IFE's critical advantage: it achieved 100% detection of monoclonal gammopathies compared to only 69.6% detection by SPEP alone 3. This superior sensitivity is particularly important because:

• SPEP can miss small monoclonal components
• β-migrating M-proteins are often hidden within normal β-region constituents 6
• Low-level paraproteins in conditions like light chain amyloidosis may be undetectable by SPEP 7

What IFE Provides That SPEP Cannot:

Definitive characterization of the monoclonal protein:

• Heavy chain class (IgG, IgA, IgM)
• Light chain type (κ or λ)
• Detection of biclonal gammopathies (3.1% of cases) 5
• Identification of light chain-only disease 5

Critical Caveats:

Therapeutic monoclonal antibodies (daratumumab, rituximab, elranatamab, teclistamab, ravulizumab) can interfere with both SPEP and IFE, mimicking pathological monoclonal proteins 8. Always document current biologic therapies before interpretation.

Communication is key: Direct dialogue between laboratory and clinician prevents unnecessary testing while ensuring appropriate follow-up when clinical suspicion remains high despite negative initial screening 3.

The Standard Workup Algorithm:

Per consensus guidelines 1:

1. Order SPEP + IFE together as initial screening
2. Add 24-hour urine collection for electrophoresis and immunofixation
3. Include serum free light chain assay for complete assessment
4. Perform nephelometric quantification of immunoglobulins

Bottom line: IFE is not optional when evaluating for monoclonal gammopathies—it is the reference method for confirmation and phenotyping, with demonstrated superiority over SPEP alone for detecting clinically significant disease 3, 4.