[Studying daratumumab's interference in serum protein electrophoresis: two case reports].

An 86-year-old woman is monitored for IgA λ-associated multiple myeloma, treated in second intention with dexamethasone, revlimid and daratumumab after a relapse. A control serum protein electrophoresis detects the presence of a new monoclonal spike, later confirmed by immunofixation as an IgG κ. Suspecting an interference due to the immunotherapy, a daratumumab specific immunofixation reflex assay (DIRA) is performed, with the addition of anti-daratumumab antibodies, confirming the interference. A second multiple myeloma case is presented, describing interference with daratumumab co-migrating with the original monoclonal immunoglobulin. Based on these cases, we propose an algorithm of action to confirm the interference and provide an accurate biological result consistent with the therapeutic and clinical context.