Distinguishing Drug from Disease by Use of the Hydrashift 2/4 Daratumumab Assay

Abstract

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.

Fig. 1.. Examples in which the patient's M protein and an additional IgGκ band (marked with an arrow) are visible by IF.

The IF result (left) for a patient with an IgAλ M-protein. When run on the Hydrashift assay (right), the IgGκ band disappears, and the daratumumab–antidaratumumab complex appears as a broad smear in the α region (highlighted with box) (A). The result indicates that the IgGκ band visible on IF was daratumumab. The IF result (left) for a patient with an IgGκ M protein with a different migration pattern than daratumumab (B). The Hydrashift result (right) shows the presence of 2 IgGκ bands and a faint daratumumab–antidaratumumab complex (highlighted with box and *). This result indicates the presence of an oligoclonal IgGκ that comigrates with daratumumab.

Fig. 2.. Examples in which a single IgGκ band is visible by IF.

The IF result (left) for a patient with an IgGκ M protein that comigrates with daratumumab (A). The Hydrashift result (right) shows the IgGκ band and the daratumumab–antidaratumumab complex in the α region (highlighted with box), indicating that the patient's M protein is still present after daratumumab has been shifted. The IF result (left) from a patient with a history of IgGκ myeloma but whose original serum studies were not available for comparison (B). The Hydrashift result (right) shows the disappearance of the IgGκ band and appearance of the daratumumab–antidaratumumab complex (highlighted with box). This indicates that the band visible on standard IF was due entirely to daratumumab and that the patient's disease is not detectable.