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Delayed hemolytic transfusion reactions (DHTR) are a potentially life-threatening complication of alloantibody formation (alloimmunization) secondary to red blood cell (RBC) transfusion. Patients requiring regular RBC transfusions, especially those with an increased risk of alloimmunization (e.g., sickle cell disease [SCD]), are especially vulnerable to severe DHTRs. Because 4%–11% of transfused SCD patients are believed to develop DHTR, and similarities in clinical symptoms between SCD-related pain crises and DHTR can diminish clinical recognition of DHTR, there is suspicion that DHTR add excess morbidity and mortality to patients with SCD. However, real-world evidence quantifying clinical outcomes and healthcare resource use among SCD patients experiencing DHTR is limited. Cerner Real-World Data, a deidentified US electronic health record database including >100 million patients, was used to identify all encounters (1/2011–12/2021) with patients aged ≥12 years with a diagnosis of SCD. Diagnosis of DHTR was based on ICD-9/10 codes or ≥1 laboratory result (using Logical Observation Identifiers Names and Codes) occurring 2–45 days post-transfusion. The index was the primary encounter where DHTR was diagnosed. The study population was restricted to patients with available data for ≥1-year pre- and 1-year post-index. Outcomes of interest included 1-year mortality post-index and the number of inpatient hospital days and pain crises among survivors 1-year pre- versus 1-year post-index. There were 27,548 patients ≥12 years with SCD, of whom 113 had a diagnosis of DHTR (471 encounters). Of these, 75 patients met the data availability inclusion criteria and were examined as the final cohort, with mean (SD) age of 29 (16). The majority of patients were female (n = 46 [61%]), Black (n = 66 [88%]) and lived in the South (n = 50 [67%]). The median number of inpatient hospital days was higher during the year following DHTR development compared to the year before (median [IQR]: 25.0 [43.8] days vs. 10.1 [20.4] days). A comparable number of patients (n, %) experienced ≥1 sickle cell crisis in the year before and after DHTR (51, 68% and 53, 71%). In the year after DHTR, 9 patients (12%) died. Using real-world data, greater healthcare resource utilization (increased inpatient hospital days) was observed in the year after DHTR, along with 12% mortality. These findings are consistent with previous studies reporting an association between alloimmunization, poor clinical outcomes and higher costs. However, real-world data sources do not easily identify patients with DHTRs, and the causal link between alloimmunization and worse outcomes remains undescribed.