Unexpected M-protein in an Anticoagulated Patient

Questions to Consider (1) What is the mechanism of action of idarucizumab? (2) How does its chemical structure help explain the IFE findings? (3) Specifically, why does the IFE not show reactivity with either the IgG anti-serum or the anti-free kappa anti-serum? Author Contributions: All authors confirmed they have contributed to the intellectual content of this paper and have met the following 3 requirements: (a) significant contributions to the conception and design, acquisition of data, or analysis and interpretation of data; (b) drafting or revising the article for intellectual content; and (c) final approval ofthe published article.