Introduction

Mixed autoimmune hemolytic anemia (AIHA) comprises warm‐ and cold‐reactive autoantibody components whose relative contributions to hemolysis may vary over time. Because serologic findings capture the dominant phenotype at a single time point, longitudinal reassessment may be required when relapse is not concordant with the initial classification. Rituximab targets CD20‐positive B cells, whereas sutimlimab blocks the classical complement pathway through C1s inhibition [1, 2, 3, 4]. Evidence for complement‐directed treatment in mixed AIHA remains limited.

We previously reported the initial course of this same patient, in whom warm AIHA was diagnosed at presentation and cold‐triggered relapse led to reassessment as mixed AIHA, followed by hematologic improvement after rituximab [5]. The present report describes the subsequent longitudinal follow‐up. During the following winter, complement‐dominant hemolysis recurred after the previously identified κ‐restricted CD20‐positive population was no longer detectable by marrow flow cytometry. Hemoglobin increased without transfusion after sutimlimab initiation. We interpreted this episode as a cold‐ and complement‐dominant relapse within mixed AIHA rather than newly developed isolated cold agglutinin disease.