What is Immunofixation Electrophoresis (IFE)?
Immunofixation electrophoresis (IFE) is a laboratory technique that identifies and characterizes the specific type of monoclonal protein (M-protein) present in serum or urine by combining electrophoretic separation of proteins with immunoprecipitation using specific antisera against immunoglobulin heavy chains (IgG, IgA, IgM) and light chains (kappa or lambda). 1, 2
Core Function and Clinical Purpose
IFE serves as the reference method for confirming and phenotyping monoclonal gammopathies when an abnormal pattern is detected on protein electrophoresis. 2, 3 The test answers the critical question of "what type" of monoclonal protein is present, which is essential for diagnosis and classification of plasma cell disorders including multiple myeloma, monoclonal gammopathy of undetermined significance (MGUS), and AL amyloidosis. 2
How IFE Works
The technique operates through a two-step process:
- First, proteins are separated by electrophoresis based on their electrical charge and size 4
- Second, specific antibodies are applied to precipitate and identify immunoglobulin heavy chains (IgG, IgA, IgM) and light chains (κ or λ) in situ 3, 4
This combination allows precise identification of which specific antibody type and light chain the abnormal plasma cells are producing. 5
Clinical Applications in Diagnostic Workup
Serum IFE (SIFE)
The National Comprehensive Cancer Network recommends serum immunofixation electrophoresis as part of the initial diagnostic workup for all suspected plasma cell disorders. 1 SIFE must be performed even when serum protein electrophoresis appears normal if clinical suspicion remains high, as approximately 15-20% of myeloma cases produce only light chains that may not create a visible spike on standard electrophoresis. 5
Urine IFE (UIFE)
Urine immunofixation electrophoresis is performed on concentrated 24-hour urine specimens and should be done even if there is no measurable protein and even if there is no peak on urine electrophoresis. 1 Unlike serum free light chain measurement, a positive result on urine immunofixation is diagnostic for monoclonal immunoglobulin light chains. 6
Superior Sensitivity Compared to Electrophoresis Alone
IFE demonstrates consistently superior sensitivity to protein electrophoresis alone, achieving 100% detection of monoclonal gammopathies compared to only 69.6% detection by serum protein electrophoresis in recent studies. 3 This makes IFE essential for accurate diagnosis, as a normal protein electrophoresis does not rule out multiple myeloma or other plasma cell disorders. 3
Role in AL Amyloidosis Diagnosis
In AL amyloidosis specifically, IFE is critical for demonstrating evidence of a plasma cell dyscrasia, which is required alongside tissue biopsy showing amyloid deposits to establish the diagnosis. 1 The American College of Cardiology recommends both serum IFE and urine IFE as part of the diagnostic evaluation when AL amyloidosis is suspected. 1
Monitoring Disease Response
IFE is repeated as clinically indicated to confirm the persistence or disappearance of the monoclonal protein during treatment. 2 The test is particularly important for documenting stringent complete response according to International Myeloma Working Group criteria, which requires a normal free light chain ratio in addition to negative IFE. 1
Key Clinical Pitfall
In approximately 10-40% of patients with ATTR cardiac amyloidosis, there will be evidence of a plasma cell dyscrasia with presence of a monoclonal light chain without evidence of AL amyloidosis or multiple myeloma—this represents concomitant MGUS, which increases with age and affects approximately 5% of patients older than 70 years. 1 Whenever monoclonal protein testing is abnormal, collaboration with a hematologist is essential to distinguish spurious findings from true MGUS, AL amyloidosis, or multiple myeloma. 1
Complementary Testing Required
IFE does not function in isolation. The National Comprehensive Cancer Network recommends that when IFE is performed, it must be accompanied by:
- Quantitative immunoglobulin levels (IgG, IgA, IgM) to measure total concentration of each immunoglobulin class 2, 5
- Serum free light chain assay with kappa/lambda ratio 1, 5
- Serum protein electrophoresis for quantification of M-protein 1
- 24-hour urine collection for total protein, urine protein electrophoresis, and urine immunofixation 1
These tests provide different but complementary information, with IFE identifying the type of M-protein while quantitative immunoglobulins reveal immune paresis (suppression of normal immunoglobulins), an important prognostic feature. 2