Criteria – both of the following:
(1) presence of an IgM monoclonal protein
(2) higher than expected concentrations of IgA and/or IgG by a nephelometric assay
Proposed mechanisms of interference:
(1) precipitation of the monoclonal protein, including cryoprecipitates
(2) formation of antibody-antibody complexes
(3) interaction between monoclonal protein and latex particles
Recommendation proposed by Schnebelen et al:
(1) Prepare a solution of beta-mercaptoethanol (BME) and Sebia IFE Gluidil chaotropic salt solution:
(1a) 20 microliterrs of 10% BME (99% pure)
(1b) 180 microliters of the chaotropic salt solution
(1c) Mix.
(2) Add 100 microliters of this mixture to 300 microliters of patient serum.
(3) Rerun nephelometric assays, making sure first that the mixture will not damage the instrument.
If the concentrations of IgA and IgG by nephelometry are significantly lower after addition of the BME solution then interference from the IgM monoclonal protein is confirmed.
Differential diagnosis:
(1) biclonal gammopathy (IgM and IgG, IgM and IgA)
(2) IgM gammopathy plus polyclonal gammopathy
