Vitamin B12 immunoassay interference in a patient with multiple myeloma – troubleshooting in a two step reagent kit based on enhanced chemiluminescence testing

Immunoassays are widely used for quantification of serum analytes however they are subjected to interference by endogenous antibodies. The laboratory procedures used to identify these endogenous antibodies is the demonstration of response to dilution or use of nonimmunoglobulin protein to block the interfering antibodies or the use of an alternate immunoassay. We report a clinical-diagnostic situation where serum vitamin B12 determination was interfered in an immunoassay due to excess of endogenous antibodies from monoclonal gammopathy that resulted in excess of analyte concentration. Reporting of such cases may be beneficial when assaying sera of multiple myeloma to avoid false results and in addition to avoid costs due to unnecessary repeat testing and further delay reporting of results.