When is additional RhIG required?

The Transfusion Safety Officer at a large community teaching hospital in Canada reports that they issue 300 µg doses of RhIG for all routine indications (and more if indicated by fetal cell screening test). They have received a request from their obstetrical nursing staff to "supply a simple rule for when repeat doses of RhIG are required if the patient has had a recent injection."

By way of example, "if a patient has received RhIG in ER on Monday for a threatened abortion and is then admitted to the hospital for a D&C on Thursday, do they need a second RhIG post D&C? Or if a patient has received RhIG following amniocentesis and then returns two weeks later for a termination, do they require a second dose of RhIG?" She has searched the literature and product monographs and has not found reference to these scenarios.

How is this handled at your facility? Is there a simple rule to determine RhIG dosing, or is it best calculated on a case by case basis?

Any "simple" rule would have to handle doses for abortion, amniocentesis chorionic villus sampling, and routine dosing during pregnancy. She asks "Does prior RhIG equate to forgoing additional RhIG for all patients who have received a full 300 µg dose within the previous few weeks? If so, what is the time limit before additional RhIG is required?"

She adds that "any insight you can provide is greatly appreciated."

ADDENDA Jan. 1, 2008

1. A Scientific Training Coordinator of the National Blood Service (Liverpool) in the UK suggests that perhaps the latest UK guidelines could offer some support to the Canadian colleague. These guidelines can be found HERE.

ADDENDA Jan. 9, 2008

2. Paul Holland, MD offers the following comment regarding the discussion of when enough RhIg has been administered. "A venous sample could be drawn around 3 days after the dose is injected IM or the next day if given IV. If an antibody screen reveals free anti-D, then enough has been delivered. If not, then additional RhIg should be given, as determined by a test to quantitate the amount of D+ cells circulating. This was the approach we used to prevent Rh immunization when Rh+ cells were given inadvertently, or on purpose, to a woman of child bearing potential in whom we wanted to prevent sensitization. Please note, the additional dose(s) could be given up to a month after the delivery of an Rh+ child to an Rh- mother and it will work just about as well as when given within 3 days, per a study by Pollack et al. in Transfusion around 1968.

ADDENDA Jan. 25, 2008

3. Professor John Judd comments that he disagrees with the comment above by Paul Holland regarding when enough RhIG has been given. His disagreement is based on a paper by Ness and Salamon entitled The failure of post-injection Rh immune globulin titers to detect large fetal-maternal hemorrhages. Am J Clin Path 1986 May;85(5):604-6. Accordingly, the Guidelines for Prenatal and Perinatal Immunohematology, published by the AABB, do not support Dr. Holland's comment.

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