Impact of Paraproteins on the Measurement of 25(OH)-Vitamin D in Patients with Monoclonal Gammopathies

Abstract

Introduction: Measuring serum 25-hydroxyvitamin D (VitD) levels is key to assessing mineral metabolism, especially in patients at risk of bone disorders, such as those with monoclonal gammopathies (MG), including multiple myeloma. Paraproteins produced by plasma cells have been observed to interfere with the automated immunoassays used to quantify VitD, generating falsely increased or decreased results, which leads to diagnostic and therapeutic risks. Treatment of samples with 25% polyethylene glycol (PEG) has been proposed as a tool to precipitate immune complexes and paraproteins, improving the specificity of the assays. Aim: The objective of this study was to evaluate the interference of paraproteins in the measurement of VitD in patients with MG, before and after treatment with PEG, and to analyze the relationship between the type and concentration of immunoglobulins with the percentage of VitD decrease. Materials and Methods: Prospective cross-sectional study in patients with and without GM (control group). Measurements were performed on the Alinity platform (Abbott), processing samples before and after PEG treatment. Results: 56% of patients with GM presented a decrease greater than 30% in VitD levels after PEG treatment, a phenomenon not observed in controls. A positive correlation was found between the percentage of decrease and Immunoglobulin G concentration. Conclusions: It is recommended to carefully interpret VitD values in patients with GM and to consider PEG treatment in suspected cases of interference.