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When first developed in the 1960s, RhIg was believed to work by a simple clearance mechanism, i.e., by coating D-positive fetal red cells with IgG anti-D, which resulted in clearance of the sensitized cells in the spleen by macrophages with receptors for IgG.Current research shows that a simple model of antigen clearance by antibody-sensitized D-positive RBCs is not the mechanism of anti-D suppression by RhIg. More is involved at the molecular level, possibly involving a down-regulation of antigen-specific B cells and related mechanisms.Regardless, if given soon enough following exposure to D+ red cells, and in a suitable dosage, RhIg has the ability to prevent immunization to D.

When first developed in the 1960s, RhIg was believed to work by a simple clearance mechanism, i.e., by coating D-positive fetal red cells with IgG anti-D, which resulted in clearance of the sensitized cells in the spleen by macrophages with receptors for IgG.Current research shows that a simple model of antigen clearance by antibody-sensitized D-positive RBC is not the mechanism of anti-D suppression by RhIg. More is involved at the molecular level, possibly involving a down-regulation of antigen-specific B cells and related mechanisms (see Further Reading).

The symptom most commonly associated with a delayed hemolytic transfusion reaction (DHTR) is unexplained decrease in hemoglobin and hematocrit. Patients may also present with fever and jaundice. Hemolysis occurs slowly and is primarily extravascular. Unlike an acute hemolytic transfusion reaction (AHTR), hemoglobinuria, acute renal failure, and disseminated intravascular coagulation (DIC) are not generally seen. On some occasions, patient's may not present with any symptoms. Serologic findings include a positive direct antiglobulin test (DAT) and/or a positive antibody screen in post-transfusion testing. In many cases, the physician will send a request for an additional transfusion because of the decreased hemoglobin levels, and not suspect a DHTR. The positive antibody screen will trigger an investigation including antibody identification. The DAT may have a mixed field appearance because of the antibody-sensitized transfused red cells and the non-sensitized patient red cells. Segments from the donor unit can be tested for the offending antigen once the antibody has been identified.Antibodies that are most often reported as the cause of DHTR are anti-Jka and anti- Jkb. Other antibodies that are also commonly implicated in a DHTR include Kell, Rh, and Duffy system antibodies.The patient's physician should be notified so that additional clinical and laboratory evidence can be evaluated.