Immuno-hematological findings in Delayed Hemolytic Transfusion Reaction (DHTR).

Sickle cell disease (SCD) is the most prevalent genetic disorder in France. Many other countries are also affected. Transfusion is still a key treatment for patients suffering from this condition. As a result, SCD patients are much more exposed to transfusions and their risks than the general population. The most feared situation is delayed hemolytic transfusion reaction (DHTR). In certain situations, defined as hyperhemolysis, autologous red blood cells (RBCs) are also targeted and destroyed. This can put the patient in a life-threating situation. Further transfusions worsen the hemolysis. As DHTR will mimic a new or resistant vaso-occlusive crisis, it can be easily underdiagnosed. SCD patients are more likely to be alloimmunized than the general population, due to discrepancies between the recipient's and donor's RBCs phenotypes. Furthermore, they are often transfused in an inflammatory state, and they also frequently harbor partial antigens in the RH system. SCD patients are more prone to develop a new alloantibody than the general population. As a result, patients with DHTR often have complex mixtures of allo and autoantibodies; RH antibodies and those considered as irregular natural antibodies are frequent. Nevertheless, about a third of DHTRs are reported in patients with no previous history of immunization. In addition, a third of SCD patients will not develop an antibody after a DHTR. The evanescence of the antibodies is important. In several studies, DHTRs were reported only in patients who were occasionally transfused. Identifying patients at risk of developing a DHTR is key to managing them properly.