The identification of monoclonal components requires the use of protein electrophoresis, immunofixation electrophoresis of serum and urine and serum free light chain measurement. The combination of these three tests grants the highest diagnostic performance in different clinical settings. In clinical practice, the monoclonal protein (M-protein) is detected in a patients’ serum or urine by the appearance of a distinct protein band migrating within regions typically occupied by immunoglobulins. Immunofixation or immunotyping then provides evidence that the identified protein band is an intact immunoglobulin or an immunoglobulin light chain. Taking into consideration that each M-protein is composed by a sequence of amino acids pre-defined by somatic recombination unique to each clonal plasma cell, the molecular mass of the M-protein can act as a surrogate marker of the protein composition. The Mayo Clinic researchers established mass spectrometry-based methods to assign molecular mass to the monoclonal immunoglobulin light chain and used this to detect the presence of M-proteins. The first method proposed is based on the enrichment of serum for immunoglobulins, followed by reduction to separate light chains from heavy chains, followed by microflow LC-ESI-Q-TOF mass spectrometry. The second method is based on the enrichment of nanobodies and the subsequent analysis on a matrix-assisted laser desorption mass spectrometer (MALDI). Both methods demonstrated a comparable diagnostic sensitivity to the standard procedures and could be considered as a possible future substitution of immunofixation.
ASJC Scopus subject areas
- Clinical Biochemistry
- Medical Laboratory Technology
- Biochemistry, medical