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Background: Daratumumab, a monoclonal antibody used to treat relapsed or refractory multiple myeloma, can interfere with protein electrophoresis and immunofixation assays. False-positive immunofixation results due to daratumumab can cause uncertainty regarding the status of a patient's disease and lead to potential misclassification of their response to therapy. The Hydrashift 2/4 Daratumumab assay (Sebia) was recently cleared by the Food and Drug Administration for resolving daratumumab interference on immunofixation. Here, we evaluate the performance of the Hydrashift assay in multiple myeloma patients receiving treatment with daratumumab-based regimens., Methods: Waste serum samples from multiple myeloma patients (n = 40) receiving daratumumab were analyzed by standard immunofixation and the Hydrashift assay. Results from these tests were compared and were evaluated along with pretreatment serum protein electrophoresis and immunofixation results, if available., Results: The Hydrashift assay shifted the migration of daratumumab in patient samples. In 27 cases, the patient's M protein was distinguishable from daratumumab by standard immunofixation. In these cases, the Hydrashift assay confirmed that the IgGκ band was daratumumab and helped identify the presence of treatment-related oligoclonal bands. There were 11 instances in which the patient's IgGκ M protein comigrated with daratumumab. In all 11 cases, the Hydrashift assay confirmed the presence of residual M protein. Finally, in 2 patients whose pretreatment immunofixation results were not available, the Hydrashift assay confirmed that the IgGκ band visible on immunofixation was due to daratumumab alone., Conclusions: The Hydrashift 2/4 Daratumumab assay is a useful tool to clarify the source of an IgGκ band on immunofixation and allow a patient's M protein to be viewed without interference., (© 2018 American Association for Clinical Chemistry.)