Transfusion of red blood cells (RBC) remains a primary treatment modality in patients with sickle cell disease (SCD). Repeated exposure to alloantigens on transfused RBCs can lead to alloantibody formation that can increase the risk of delayed hemolytic transfusion reaction (DHTR). 1 The incidence of DHTR in transfused adult SCD patients ranged from 4.8-7.7% during a 30-month and 5-year study period, respectively. 2,3 The case fatality rate is 6%. 4 The symptoms of DHTR typically appear 7-14 days post-transfusion and include generalized pain, hemoglobinuria with/without fever, a significant drop of total hemoglobin and hemoglobin A from the post-transfusion value and suboptimal reticulocyte response. These clinical features mimic a classic vaso-occlusive pain crisis (VOC), further confounding the detection of DHTR. In addition, patients can experience hyperhemolysis, evidenced by hemolysis of both native and transfused RBCs. General management of DHTR depends on the extent of hemolysis and the patient's clinical condition, from supportive care strategies to high dose erythropoietin, intravenous immunoglobulin (IVIg), and immunosuppression. 4,5 We report here comprehensive data on a 14-year-old African American female with SCD (β s β s genotype) and evidence for alternative complement pathway (ACP) activation during two of her three DHTR hyperhemolysis episodes, one of which had no new detectable allo-or autoantibody. This patient's past medical history is significant for multiple episodes of acute chest syndrome (ACS) and VOC, and an episode of acute splenic seques-

The clinical efficacy of hydroxyurea in patients with sickle cell anemia (SCA) has been well established. However, data about its clinical effectiveness in practice is limited. We evaluated the clinical effectiveness of hydroxyurea in a large pediatric population using a retrospective cohort, pre-post treatment study design to control for disease severity selection bias. The cohort included children with SCA (SS, S β 0thalassemia) who received care at Children's Healthcare of Atlanta (CHOA) and who initiated hydroxyurea in 2009-2011. Children on chronic transfusions, or children with inadequate follow up data and/or children who had taken hydroxyurea in the 3 years prior were excluded. For each patient, healthcare utilization, laboratory values and clinical outcomes for the 2-year period prior to hydroxyurea initiation were compared to those 2 years after initiation. Of 211 children with SCA who initiated hydroxyurea in 2009-2011, 134 met eligibility criteria. After initiation of hydroxyurea, rates of hospitalizations, pain encounters, and emergency department visits were reduced by 47% (<0.0001), 36% (p=0.0001) and 43% (p<0.0001), respectively. Average hemoglobin levels increased by 0.7g/dl (p<0.0001). Hydroxyurea effectiveness was similar across gender, insurance types and age, although there was a slightly greater reduction in hospitalizations in younger children.