74-Year-old female with new monoclonal protein on serum immunofixation electrophoresis

- Daratumumab and other mAb therapeutics can appear as M-proteins on SPEP and IFE.
- mAb interference can be erroneously diagnosed as disease progression, class switching, development of a new clone, or MRD.
- Strategies to identify interference include characterizing mAb elution sites and active communication with clinicians.
- Specialized assays such as DIRA may help resolve cases of co-migrating disease M-protein and mAb.
- New protein MS assays may also be developed to unambiguously identify mAbs.