Red Blood Cell - IMProving trAnsfusions for Chronically Transfused recipients (RBC-IMPACT) is an observational cohort study to assess donor, component, and recipient factors that contribute to RBC efficacy in chronically and episodically transfused patients. The objective of the study is to determine how specific genetic and non-genetic factors in donors and recipients may impact RBC survival after transfusion - in short, what factors on both the donor and recipient side may improve the efficacy of the transfusion.

Sickle cell disease (SCD) and thalassemia are genetic disorders inducing anemia of differing pathophysiology. A primary therapy for preventing certain SCD complications (e.g., stroke) and for thalassemia major is regular red blood cell (RBC) transfusion, coupled with iron chelation to prevent the complications of transfusion-induced iron overload. For patients with pediatric hematology-oncology diagnoses with chemotherapy-induced aplasia, RBC transfusion is also common, but the degree of transfusion-induced iron overload and its implications for these patients is incompletely understood. Because iron-related tissue toxicity is a major cause of morbidity and mortality in regularly transfused patients, developing strategies to minimize iron loading and iron toxicity is a key objective of this proposal (study Aim #2), stemming from the objective to optimize RBC unit characteristics that patients with SCD and thalassemia receive beyond RBC phenotype matching for Rh C, E and K antigens (study Aim #1). The study will enroll patients with SCD, thalassemia or pediatric oncologic diagnoses receiving eligible transfusion at 6 hospital sites in the United States, as well as patients with SCD at 5 hemocenters in Brazil.

Inclusion Criteria (Aim #1):

• Well-characterized transfusion-dependent form of SCD or thalassemia (including Hemoglobin E-thalassemia and sickle-beta thalassemia) on chronic simple transfusion therapy or partial manual exchange
• On a regular simple RBC transfusion schedule, including partial manual exchange (i.e., 1-3 units scheduled every 2-6 weeks and on a minimum 6-month chronic transfusion trial; for partial manual exchange, the phlebotomy must be completed before the transfusion is started without a back and forth between rounds of phlebotomy and transfusion)
• Seen at any participating domestic hub hospital (i.e., Columbia University Irving Medical Center/Morgan Stanley Children's Hospital of New York, Weill Cornell Medical Center/Komansky Children's Hospital, Boston Children's Hospital, Froedtert & Medical College of Wisconsin/Children's Wisconsin, University of California San Francisco, Benioff Children's Hospital Oakland) or enrolled in the Brazil REDS-IV-P sickle cell disease cohort and seen at any participating Brazil hemocenter (i.e., Childrens Institute and Adult Clinics at Hospital das Clínicas da Faculdade de Medicina da Universidade de São Paulo - HCFMUSP, HEMOAM - Amazonas, HEMOMINAS - Minas Gerais, HEMOPE -Pernambuco, and HEMORIO - Rio de Janeiro)

Exclusion Criteria (Aim #1):

• Institutionalization or imprisonment
• Foster care
• Weight <11 kg

Inclusion criteria (Aim #2):

• Either included in Aim #1 (consented patient with SCD or thalassemia) or patient with pediatric oncologic diagnosis under care in a pediatric hematology/oncology service with anemia due to chemotherapy or primary/secondary hypo-proliferative bone marrow requiring a RBC transfusion (including HSCT)
• [In domestic study only] Age ≤21 years old (many pediatric services include care of patients up to age 21, therefore the protocol will not limit by age but instead on whether they are seen in a pediatric service)
• Planned transfusion of RBC from an aliquot or unit from a single donor
• Seen at any participating domestic hub hospital (i.e., Columbia University Irving Medical Center/Morgan Stanley Children's Hospital of New York, Weill Cornell Medical Center/Komansky Children's Hospital, Boston Children's Hospital, Froedtert & Medical College of Wisconsin/Children's Wisconsin, University of California San Francisco, Benioff Children's Hospital Oakland) or at any REDS-IV-P participating Brazil hemocenter (i.e., Childrens Institute and Adult Clinics at Hospital das Clínicas da Faculdade de Medicina da Universidade de São Paulo - HCFMUSP, HEMOAM - Amazonas, HEMOMINAS - Minas Gerais, HEMOPE -Pernambuco, and HEMORIO - Rio de Janeiro).

Exclusion criteria (Aim #2):

• Institutionalization or imprisonment
• Foster care
• Current active auto-immune hemolytic anemia based on positive direct antiglobulin test (DAT) with laboratory evidence of hemolysis and increased transfusion requirement
• [In domestic study only] Microangiopathic hemolytic anemia
• Weight <18 kg

All transfused patients with sickle cell disease (in the U.S or Brazil) and thalassemia on simple chronic transfusion (or partial manual exchange transfusion) from hospitals affiliated with REDS-IV-P Domestic hubs or Brazil hemocenters. (Aim #1)

Chronically transfused patients with sickle cell disease or thalassemia, and patients with pediatric oncology diagnoses with hypo-proliferative bone marrow receiving care at hospitals affiliated with REDS-IV-P Domestic hubs or Brazil hemocenters (for SCD only). (Aim #2).

De-identified public use datasets will be created and delivered to NHLBI at the end of the study (and end of the REDS-IV-P program) and will be made available indefinitely for future analysis

At the end of the REDS-IV-P program, estimated in March 2026, the public use data sets will be available and will be available indefinitely for future analytic use.

Public use datasets will be posted to NIH/NHLBI data repository systems.