This blood derivative, issued at PMH through the blood bank, consists of anti-D (IgG) harvested from special immunized donors with high antibody levels via plasmapheresis. It has never been shown to transmit infectious disease. The only dose size stocked at PMH is the 300 µg size that can be adminstered only through an intramuscular route. It comes in a prepackaged syringe in about 1ml of fluid. This size is the standard full size dose. PMH does not stock the "micro" dose which is a 50 µg dose for first trimester use only (small exposures).
One 300 µg dose is enough to protect an Rh negative individual from anti-D formation when exposed to up to 15 ml of RBCs or 30 ml of whole blood.
Intravenous Rh immune globulin (WinRho SD) is available for use in preventing Rh alloimmunization. However, it is much more expensive than the intramuscular injected RhoGAM. Routine use of IV RhIg instead of IM RhIg should be discouraged except in special circumstances (see below "Use following platelet transfusion").
Use in pregnancy. RhIG is administered to Rh negative women who are pregnant (or recently delivered) and do not already have alloimmunization to the D antigen. Routinely one vial is administered at 28 weeks of gestation and a second within 72 hours following delivery. These time recommendations are somewhat arbitrary. RhIG can and should be administered even if 4 or 5 days have elapsed since delivery. No one is really sure when the time cut-off for effectiveness is, so it's best to go ahead and give it just to be sure. Additional vials of RhIG may be indicated at the time of delivery if a larger-than-normal fetomaternal hemorrhage occurred. See the section on fetomaternal hemorrhage detection for further details.
RhIG is also indicated at the time of ectopic pregnancy, amniocentesis, abortion or miscarriage, or abdominal trauma in Rh negative, unimmunized women.
RhIG is IgG antibody. It will cross the placenta and can cause a
weakly positive DAT in the fetus/infant. However, the titer of anti-D
is too weak to cause any clinically significant RBC destruction. An
Rh negative woman administered RhIG will generally develop a
detectable anti-D with a titer in the range of 1 to 4. Occasional
women sampled right after RhIG administration may have a titer of up
to 8. Any higher titer of anti-D should be considered suspicious of
true alloimmunization. However, if there is doubt as to whether an
anti-D detected prenatally represents true alloimmunization or not,
further RhIG probably should be administered at the time of delivery
to make sure.
The anti-D of RhIG can be detected in some women for 3 to 5 months
after administration of RhIG.
Use following platelet transfusion. RhIG may be administered to Rh negative recipients of Rh-positive platelet transfusions to avoid anti-D formation. The option to use RhIG in these situations is generally left up to the physician. You may want to remind the physician that such an option is available, but often the clinician chooses not to give the RhIG and that's alright. Sometimes they are worried about giving an IM shot to someone who's severely thrombocytopenic, and other times they don't want to administer the RhIG because the patient is so young (RhIG is not recommended for babies). Another option to be considered is the administration of 300µg of intravenous Rh immune globulin (WinRho SD). Many times a very sick patient will not make alloantibodies anyway. One vial of RhIG (300µg) should protect against alloimmunization from up to 30 platelet concentrates (or roughly 3 apheresis units). Each platelet concentrate, unless grossly bloody, should contain less than 0.5 ml of RBCs.
Use following RBC transfusion. Generally, we do not advocate giving RhIG to an Rh negative patient who just received an Rh positive RBC transfusion. The dose of RhIG needed to cover the exposure is too great, the expense and discomfort would be high, and there is little scientific evidence that it will work for such large exposure anyway. Doing the calculations, transfusion of just one unit of Rh positive RBCs (RBC volume 200 ml, say) would require the administration of 14 vials of RhIG [200ml ÷15ml per vial = 13.3 vials]. Exceptions might be made in rare cases; for example a young woman who happened to get just one unit of Rh positive RBCs.
Return to Blood Components/Derivatives
Table of Contents
Return to Transfusion Medicine Table of
Contents
Return to Call Manual Table of
Contents