Alleviation of IgM Monoclonal Protein Interference in Nephelometric Assays by Sample Treatment With Reducing Agent in a Chaotropic Salt Solution: Table 1

Abstract

In some patients, the presence of monoclonal IgM proteins can cause substantial false elevation in nephelometric assays. A 59-year-old woman with previously unrecognized Waldenström macroglobulinemia had high serum viscosity. Nephelometric analysis revealed elevated measured concentrations of IgG, IgA, and IgM. Pretreatment with a reducing salt solution yielded resolution of cross-linked immunoglobulins into a distinct IgM κ monoclonal protein band by immunofixation electrophoresis. Measured quantitative immunoglobulin measurements in treated and untreated specimens were compared. An approximately 50% drop in IgG and IgA concentrations was observed in the presence of reducing agent, while IgM concentrations were unchanged. We report that the addition of reducing agent solution can alleviate artifactual elevation of nephelometric determination of IgG and IgA concentrations. These results are consistent with dissociation of higher order IgM complexes, leading to reduction of nonspecific light scattering by IgM complexes in IgA and IgG nephelometric reactions.

Paraprotein interference with turbidimetric gentamicin assay

“…Serum protein abnormalities have been shown to interfere with turbidimetric assays such as vancomicin on the Beckman DxC800 general chemistry analyzer ( 5 ). Interferences have also been reported with other turbidimetric assays, C-reactive protein ( 6 , 7 ) phenytoin ( 8 ), and transferrin ( 9 ), as well as with nephelometric assays, IgA and IgG ( 10 ), and other non turbidimetric/nephelometric assays such as total bilirubin ( 11 ), thyroid-stimulating hormone ( 12 ), lactate dehydrogenase, uric acid and alkaline phosphatase ( 13 ), glucose and gamma-glutamyl transferase ( 14 ), HDL-cholesterol and as well as glucose interference being observed with glucose analyses on a hexokinase method but not on an oxidase method ( 15 ). From our searches no such interferences have been reported with gentamicin.…”

Prognostic Contribution of the New Immunoglobulin (Ig) Biomarkers (Freelite™ and Hevylite™) in Waldenstrom’s Macroglobulinemia (WM)

“…Thus IgM detection, including quantification by serum protein electrophoresis, densitometry and immunofixation, is mandatory for d iagnosis and monitoring of WM patients. The accuracy of the tests depends upon the position of the migrat ing monoclonal protein, the quantificat ion of which requires skilled personnel [10][11][12]. Furthermore, user operator error may account for unexpected results particularly at lo w concentration.…”