Diagnostic Approach for Monoclonal Protein Spike

Initial Evaluation

The International Myeloma Society recommends serum immunofixation electrophoresis (IFE) and serum free light chain assay as the next most appropriate tests for a patient with a monoclonal protein spike, to confirm the presence and identify the type of monoclonal protein 1, 2
Serum free light chain (FLC) assay should be ordered simultaneously to detect unbound free light chains and determine the κ:λ free light-chain ratio, which can detect clonality through an abnormal κ:λ ratio 1
24-hour urine collection with urine protein electrophoresis and immunofixation is necessary to quantify and characterize any urinary monoclonal proteins, according to the American Society of Clinical Oncology 2, 3

Immunofixation is more sensitive than protein electrophoresis for detecting small amounts of monoclonal proteins, as stated by the National Comprehensive Cancer Network 1
IFE is essential for typing the monoclonal protein (IgG, IgA, IgM, κ, λ) which has important diagnostic and prognostic implications, according to the European Society for Medical Oncology 4
The serum free light chain assay can detect clonality through an abnormal κ:λ ratio and is particularly valuable in detecting light chain-only disorders that may be missed by electrophoresis alone, as recommended by the International Myeloma Society 1, 2

If the monoclonal protein is ≥3 g/dL (for IgG or IgA) or if there are concerning clinical features, a bone marrow aspirate and biopsy should be performed, according to the American Society of Hematology 5
Bone marrow examination should include assessment for percentage of plasma cells, with CD138 staining when possible, and cytogenetic studies (conventional karyotyping and FISH) should be included as part of the bone marrow evaluation, as stated by the National Comprehensive Cancer Network 3
Complete blood count, serum calcium and creatinine, and serum β2-microglobulin and lactate dehydrogenase should be assessed to evaluate for anemia, hypercalcemia, renal impairment, and prognostic information, according to the European Society for Medical Oncology 2, 3

For patients with MGUS, risk stratification should be performed based on monoclonal protein concentration, type of immunoglobulin, and serum free light chain ratio, as recommended by the International Myeloma Society 1, 3, 7
Higher risk patients require closer monitoring, according to the American Society of Clinical Oncology 5