Delayed hemolytic transfusion reaction (HTR) results from a secondary (anamnestic) immune response that causes a weak, undetectable antibody to become stronger.
Upon re-stimulation by the donor, red blood cells positive for the antigen corresponding to the patient's antibody:
- Patient's memory B cells differentiate into antibody-producing plasma cells.
- As a new IgG antibody is produced, it sensitizes antigen-positive transfused donor red blood cells.
- The IgG-sensitized donor red blood cells are removed by extravascular hemolysis (EVH), mainly in the spleen.
