The risk of transfusion-transmitted infectious disease is now significantly reduced, and serious non-infectious hazards have become the most common complication of blood transfusion. Hemolytic transfusion reactions New blood matching technologies have greatly reduced the risk of blood group incompatibility transfusion, but it is still difficult to completely eliminate. According to the U.S. FDA, ABO blood group incompatibility accounted for 7% of transfusion-related deaths in 2005 and 2006, and other blood group incompatibility accounted for 20%. In addition to the familiar acute hemolytic transfusion reactions, hemolytic transfusion reactions also include late hemolytic transfusion reactions that can be easily overlooked and occur only 3-10 days after transfusion. Patients may have been immunized against secondary red blood cell antigens (e.g. Rh, Kidd system antigens) due to previous pregnancies or transfusions, and the resulting alloantibodies are too low in concentration to be screened for prior to transfusion. When red blood cells with these antigens are reintroduced, the body rapidly undergoes a memory reaction resulting in a delayed hemolytic transfusion reaction. The incidence of delayed hemolytic transfusion reactions is low and the symptoms are not as severe as those of acute hemolytic transfusion reactions, but the incidence may be as high as 36% in patients with sickle cell disease, where the patient’s own red blood cells hemolyze along with the imported red blood cells and the symptoms are severe and potentially fatal. Graft-versus-host disease When blood products containing immunoreactive T lymphocytes are transfused, immunodeficient recipients or recipients who share an HLA haplotype with the donor are unable to recognize and clear these allogenic lymphocytes. The heterologous lymphocytes that colonize and proliferate in the body produce an immune response to the host’s skin, gastrointestinal tract and liver tissues, causing severe symptoms such as fever, rash, diarrhea, liver function impairment and complete blood cytopenia. Due to the lack of effective treatment, transfusion-associated graft-versus-host disease has a mortality rate of more than 90%, so prevention is important for this disease. Patients with congenital immunodeficiency syndrome, after hematopoietic stem cell or solid organ transplantation, hematologic tumors such as lymphoma, other solid tumors, as well as intrauterine transfusion or blood exchange, and premature infants are at high risk for this disease. In addition, blood transfusion between first- or second-degree relatives is also a high-risk factor for the disease. However, patients with HIV/AIDS are not a risk group for the disease. Irradiation of blood products with gamma radiation is currently the only effective method of preventing transfusion-associated graft-versus-host disease. Iron overload The total iron content of normal adults is 50 mg/kg for men and 35 mg/kg for women, but the body lacks an effective mechanism for iron excretion except for menstruation and loss of iron by epithelial cell shedding. If transfusion-dependent anemic patients receive 2U of red blood cells every 2 weeks, they will receive 50U for 1 year and 200U for 4 years, which is equivalent to an intake of 20g of iron, 7 times the total iron content of normal adults, i.e. it may cause secondary hemochromatosis. Thalassemia, hereditary anemia, and acquired anemia themselves have iron overload due to ineffective hematopoiesis and other mechanisms, and transfusion dependence causes a large amount of exogenous iron to enter the body, resulting in damage to important organs including the liver, heart, spleen, pancreas, thyroid, and pituitary gland. Expert consensus and guidelines for the treatment of transfusion-induced iron overload have been developed in many countries and regions. It is recommended that iron removal therapy should begin with transfusion of red blood cells up to 120 ml/kg and a serum ferritin (SF) consistently above 1000-2000 ng/ml. Once treatment is started, SF should be maintained below 1000ng/ml. Iron removal is carried out by iron chelation therapy, and the three iron chelating agents are desferrioxamine (DFO), desferrioxone (DFP) and desferrioxylate (DFX). Immunomodulation The prolonged survival and increased viability of the transplanted kidney after renal transplantation in patients with a history of blood transfusion was discovered in 1973, and it was later found that the imported leukocytes played a key role in this. This transfusion produces a series of responses involving immunomodulation known as transfusion-associated immunomodulation. With the modern use of various novel immunosuppressive agents in the clinic, transfusion of allogeneic red blood cells is no longer required to improve graft survival. In addition, many studies have identified adverse effects of transfusion-associated immunomodulation, including increased rates of postoperative infection with perioperative transfusion and early recurrence and metastasis of tumors that may be associated with transfusion. Acute lung injury The US FDA reports that transfusion-related acute lung injury is the most common cause of transfusion-related death, occurring at 1 case per 5,000 transfusions, with a mortality rate of 15%. The clinical presentation is sudden onset of dyspnea, foamy sputum, severe pulmonary edema, cardiac panic, fever, and severe hypoxemia during or within 6 hours after transfusion. The occurrence of transfusion-associated acute lung injury is associated with granulocyte antibodies contained in the blood product, and the exact mechanism is unknown. Treatment lies in early diagnosis and aggressive respiratory support.