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  • Title: Monitoring free light chains in serum using mass spectrometry.
    Author: Barnidge DR, Dispenzieri A, Merlini G, Katzmann JA, Murray DL.
    Journal: Clin Chem Lab Med; 2016 Jun 01; 54(6):1073-83. PubMed ID: 26845720.
    Abstract:
    BACKGROUND: Serum immunoglobulin free light chains (FLC) are secreted into circulation by plasma cells as a by-product of immunoglobulin production. In a healthy individual the population of FLC is polyclonal as no single cell is secreting more FLC than the total immunoglobulin secreting cell population. In a person with a plasma cell dyscrasia, such as multiple myeloma (MM) or light chain amyloidosis (AL), a clonal population of plasma cells secretes a monoclonal light chain at a concentration above the normal polyclonal background. METHODS: We recently showed that monoclonal immunoglobulin rapid accurate mass measurement (miRAMM) can be used to identify and quantify a monoclonal light chain (LC) in serum and urine above the polyclonal background. This was accomplished by reducing immunoglobulin disulfide bonds releasing the LC to be analyzed by microLC-ESI-Q-TOF mass spectrometry. Here we demonstrate that the methodology can also be applied to the detection and quantification of FLC by analyzing a non-reduced sample. RESULTS: Proof of concept experiments were performed using purified FLC spiked into normal serum to assess linearity and precision. In addition, a cohort of 27 patients with AL was analyzed and miRAMM was able to detect a monoclonal FLC in 23 of the 27 patients that had abnormal FLC values by immunonephelometry. CONCLUSIONS: The high resolution and high mass measurement accuracy provided by the mass spectrometry based methodology eliminates the need for κ/λ ratios as the method can quantitatively monitor the abundance of the κ and λ polyclonal background at the same time it measures the monoclonal FLC.
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