Heterophilic antibody interference in a tryptase immunoassay

Objective Investigation of the susceptibility of a tryptase immunoassay to interference by heterophilic antibodies. Methods The effect of preincubation with a blocking agent was investigated on the levels of tryptase, human anti-mouse antibodies and IgM rheumatoid factor in sera with elevated IgM rheumatoid factor levels. Results In 5 of 30 sera with IgM rheumatoid factor, tryptase levels were reduced at least twofold after pre-incubation with blocking reagent. A significant association was observed between the presence of IgM rheumatoid factor in the sera and the interference of tryptase immunoassay. There was no quantitative correlation found between the reduction in serum tryptase level by treatment with a blocking agent, and the amount of IgM rheumatoid factor was present. However, this reduction in serum tryptase was significantly correlated with the amount of human anti-mouse antibodies in the sera. After incubation with blocking agent, there was no change in IgM Rheumatoid factor level, but a significant decrease in human anti-mouse antibodies. Conclusion The Phadia tryptase assay method, in its present form, is sensitive to interference by heterophilic antibodies.