Thirty-three-day storage of dithiothreitol-treated red blood cells used to eliminate daratumumab interference in serological testing

Background and Objectives: Daratumumab binds CD38 on red blood cells causing interference with indirect antiglobulin tests. Dithiothreitol is used to eliminate interference allowing detection of alloantibodies. Haemolysis is observed during storage of dithiothreitol-treated antibody identification panel cells. The objective of this study was to develop a modified method for dithiothreitol treatment to reduce the haemolysis during 33 days of storage and still be able to eliminate daratumumab interference. Materials and Methods: Panel cells were treated with various volumes of 0·2 m dithiothreitol supplied by various manufacturers. Haemolysis Index of dithiothreitol-treated and untreated panel cells was measured and compared on days 1, 15 and 33. Antibody screening tests with dithiothreitol-treated screening cells were performed on samples from 15 daratumumab-treated patients (dose 16 mg/kg) and 34 patients with known alloantibodies. Antibody identifications with dithiothreitol-treated panel cells were performed on seven additional known alloantibodies. Results: Dithiothreitol treatment with a ratio of 30:25 (red blood cells:dithiothreitol) showed the same degree of haemolysis as with untreated panel cells. Daratumumab interference was eliminated in all 15 samples from daratumumab-treated patients. Twenty-six of 34 alloantibodies were detected, and all seven additional alloantibodies were identified using the modified dithiothreitol treatment. Eight alloantibodies within the Kell system were negative. No decrease in the reaction strength was observed during the 33-day storage period. Conclusion: The modified dithiothreitol method was able to reduce haemolysis during storage and to detect and identify alloantibodies in the presence of daratumumab.