Abstract
Accurate detection of M-proteins in multiple myeloma (MM) patients treated with daratumumab (DARA) is challenging because DARA, an IgG-κ monoclonal antibody, produces immunofixation electrophoresis (IFE) bands that mimic disease-derived M-proteins. Although the Daratumumab-Specific Immunofixation Reflex Assay (DIRA) can resolve this interference, it is not always feasible in routine practice, highlighting the need for alternative methods. D-Clean is a novel reagent designed to neutralize DARA interference and is compatible with standard IFE systems without specialized equipment. We evaluated the performance of D-Clean compared with DIRA and examined clinical factors influencing DARA interference, including the interval since the last administration and serum IgG levels. Serum samples from 20 DARA-treated patients, 32 untreated patients, and normal serum spiked with DARA were analyzed.D-Clean eliminated DARA-derived IgG-κ bands in 19 of 20 patients, yielding results comparable to DIRA. Notably, in two cases, D-Clean detected small Bence Jones-type M-proteins that were missed by DIRA, suggesting slightly higher sensitivity. Among 76 samples from DARA-treated patients, DARA-derived bands appeared only within 33 days after the last dose and were more frequent in patients with low polyclonal IgG levels. To our knowledge, this is the first study to demonstrate that serum IgG levels significantly affect the detectability of DARA-derived bands on IFE. These findings indicate that D-Clean is a reliable and practical alternative to DIRA, although the results are preliminary and require validation in multicenter studies. For clinicians, awareness of DARA dosing intervals and patients' IgG status is essential for accurate response assessment and treatment decision-making.