Analytical interference on measurement of immunoglobulins in monoclonal gammopathy

Monoclonal gammopathy has been reported to interfere with several laboratory measurement results. We investigated potential interference in monoclonal gammopathy on immunoglobulin A (IgA), immunoglobulin G (IgG), and immunoglobulin M (IgM) concentrations using three different routine chemistry instruments: Alinity (Abbott Laboratories), Cobas 8000 (Roche Diagnostics) and Optilite (Binding Site) at the Department of Clinical Biochemistry, Aalborg University Hospital, Denmark. Blood samples collected from 216 patients with known monoclonal gammopathy were analyzed on Alinity, Cobas and Optilite. Diagnoses were ascertained from clinical records. Scatter plots with Passing-Bablok regression were used to investigate associations between concentrations of IgA, IgG and IgM measured with each of the different instruments. Furthermore, comparison of IgG analyses on Alinity, Optilite and Cobas according to monoclonal IgM concentration was explored with Bland-Altman plots. A total of 81 patients were identified with IgM type monoclonal gammopathy and 8 of these patients (10%) had analytical interference as reflected by more than 25% decrease in the level of IgG measured on Alinity as compared to Optilite and Cobas. All blood samples with interference on IgG measurement using Alinity were from patients with lymphoplasmacytic lymphoma/Waldenströms macroglobulinemia and all of them had monoclonal IgM concentrations above 10 g/L. This study identified a source of interference from IgM monoclonal gammopathy on IgG measurement performed using Alinity. The interferences caused falsely low results of IgG which is important to recognize to ensure proper patient management.