BACKGROUND: Ethylenediamine tetraacetate/glycine acid (EGA) and chloroquine diphosphate (CDP) are used in transfusion testing to dissociate IgG antibodies from red blood cells (RBCs). However, the ability of these reagents to dissociate IgM antibodies sensitized to RBCs has not been comprehensively elucidated. We investigated whether EGA and CDP could dissociate cold-reactive antibodies from RBCs and their effect on RBCs after dissociation treatment. STUDY DESIGN AND METHODS: Cold-reactive antibody-sensitized RBC samples were prepared by mixing group A RBCs and group B plasma and treated with EGA, CDP, and dithiothreitol (DTT). Before and after the dissociation treatment, changes in the agglutination of these RBCs were assessed using the test tube method. Flow cytometric analysis was used to confirm the nature of antibodies bound to RBCs. Additionally, RBC morphology was evaluated using scanning electron microscopy. This study utilized off-label use of EGA and CDP. RESULTS: Flow cytometric analysis showed that antibodies sensitized to RBCs were mainly IgM antibodies. After antibody dissociation, agglutination disappeared in the EGA-treated samples to the same degree as in the DTT-treated samples. However, IgM antibodies remained in the CDP-treated samples. Regarding RBC morphology, RBC surface appeared coarser in both EGA- and CDP-treated samples, and RBC area was significantly smaller in the CDP-treated samples than in the EGA-treated samples. DISCUSSION: EGA could dissociate cold-reactive antibodies, whereas CDP had a higher residual antibody content. This difference in dissociation ability appears to correlate with the antibody pH of the dissociation reagent. EGA treatment may be useful in cases of sensitization by high-titer cold-reactive antibodies.