A-058 Vitamin D and multiple myeloma: High concentrations of paraproteins could affect laboratory assays?

Abstract Background It is known that Immunoassays (IA) used in diagnostic laboratories are prone to interfere with antibodies of any classes present in the serum of the patients (IgA, IgG, IgM or IgE). Interferences can give either false positive or false negative results depending on the interaction with the IA. In Multiple Myeloma Disease patients (MMP), Vitamin D (VitD) measurement is recommended in phosphocalcium metabolism alterations. High concentrations of paraproteins in the serum of these patients could analytically affect the results. Objectives 1)To Evaluate the presence of interference in VitD Measurement in MMP compared to a control group. 2)To look for an association between Ig concentration, type of this and percentage (%) of post-treatment decrease VitD levels. Methods Cross-sectional and prospective study. VitD levels were measured by Chemiluminescence (Alinity-Abbott) in 48 samples: 26 MMP without VitD supplementation but positive Igs processed by Nephelometry (Beckman), 22 controls without MMP or any other autoimmune disease. VitD concentration was measured directly (DC) and after precipitation samples with PEG 25%(EC) in equal proportions to investigate the presence of interferences. A decrease % was calculated between DC and EC. Results In 11/26 (42%) samples from MMP a decrease in EC compared to DC of more than 30% was observed, maximum % value obtained in control patients (Graph). No association was observed between Ig concentration (G;M or A), type of paraproteins (?,?,?/?) and the % decrease. Conclusion Samples from MMP showed a decrease % in VitD measurement, signalling that presence of Igs could interfere for its dosage. Control patients did not exceed 30% decrease. According to our results, we suggest in MMP the systematic search of interference in VitD dosages using this methodology. in order to provide an evaluation compatible with the clinic from the laboratory.