Impact of new policies to eliminate tests for weak D on the decision to administer RhIG in pregnant women who were designated weak D on previous Rh testing protocols

A colleague reports that as of February 2 this year they will begin determining the Rh type of each adult transfusion candidate by following AABB STANDARD 5.13.2 THAT STATES THAT THE TEST FOR WEAK D IS UNECESSARY WHEN TESTING THE RECIPIENT, AND WILL ALSO FOLLOW STANDARD 5.20.3 THAT SAYS THAT A TEST FOR WEAK D IS NOT REQUIRED FOR WOMEN WHO ARE PREGNANT OR WHO HAVE RECENTLY BEEN PREGNANT AND ARE CONSIDERED FOR RH IMMUNE GLOBULIN ADMINISTRATION. The colleague's laboratory will interpret the patient as Rh positive or Rh negative based on the presence or absence of agglutination in an immediate spin typing test. Also on February 2, 2004, they will eliminate performing weak D (Du) testing of transfusion candidates. However, because the laboratory's past policy was to perform weak D (Du) testing for all patients who appeared to be Rh negative by direct agglutination testing, they anticipate (at least in the short run) that their new typing policy will lead to discovering some patients with current Rh typing results that are discrepant with historical records. They do plan to continue routine weak D testing on umbilical cord blood samples and on newborns when indicated, in order to determine if a D negative mother is a candidate for Rh immune globulin. The inquiring colleague wonders how others manage mothers whose historical records show them to be weak D positive (based on their past Rh typing protocol), but who currently type Rh negative. Should these patients receive RhIG at 28 weeks gestation and after delivering an Rh positive baby? Should the patient's physician be informed that the patient was previous called weak D positive due to a different testing scheme, and therefore not consider the patient to be a candidate for RhIG, even though currently the patient types Rh negative? These women did NOT receive RhIG in the past at the inquiring colleague's hospital, because they were considered to be Rh positive, albeit weakly so.

The following responses have been received.

ADDENDA Jan. 30, 2004

1. John Judd, at the University of Michigan (attribution used with permission) reports that his institution eliminated tests for weak D on prenatal patients (and transfusion candidates) in March of 2002. Prior to implementation of their current Rh typing scheme they distributed a letter (much like this generic notification) to their medical staff. In addition, colleagues may want to review their data (Transfusion 2002;42(S):20) on the reactivity of certain monoclonal anti-D reagents with partial D RBCs. In their facility, all samples from 'new' patients get tested twice for ABO and Rh; the second test is done with different reagents and only after the sample has been re-identified, preferably by a 2nd technologist. If one or both anti-D's are nonreactive or only weakly reactive, the patient is concluded to be Rh-negative and treated as such.
   
   They do of course test all newborns of apparent Rh-negative women for weak expression of D. If the infant tests as weak D the rosette test may be falsely negative. In such a case they go straight to the Kleihauer-Betke (KB) test on the mother to determine the volume of fetomaternal bleed, from which they base their RhIG dose. Also, they may get a diffusely positive test when they subject the RBCs of a weak D woman to the rosette test; again, they do a KB test.
   
   John had a few anecdotes to share with the e-Network Forum readership. A patient who was concluded to be Rh+ during previous pregnancies is now concluded to be Rh- and a candidate for antepartum RhIG. She refuses RhIG prophylaxis. This refusal is documented in the patient's medical records. An outside hospital that adopts a similar protocol to theirs types a pregnant woman as Rh- and her infant as Rh+ by the test for weak D; they then test the mother and she is also Rh+ by the test for weak D. They call to ask if they should give RhIG?
   
   Although it is likely the infant inherited the mother's partial D gene. the answer was, " 'tis better to err on the side of safety."
   
   Finally, there is a report of an international forum on RhIG prophylaxis (Vox Sang 2003;85:328-37) that readers might find interesting, especially in light of the recent article posted from the Society of Obstetrics and Gyneacology of Canada. It is noted that the Canadian folks state that RhIG should not be given to weak D women, and this seems to be the sense in all but two countries (USA, UK) surveyed in the Vox article.

ADDENDA Feb. 5, 2004

2. A Transfusion Medicine specialist in New Zealand wonders if reliable data exist on the effectiveness of anti-D prophylaxis in women who have a partial D state and the infant is (fully) Rh(D) positive. He also wonders if anyone has performed a survey of the opinion of women who are weak D and are fully informed on the issue of anti-D prophylaxis to see if they do, or do not, want to have Anti-D administered? He feels that this is an important issue that has been ignored.
   
   
3. In reply to the above query, the Editor consulted with John Judd, at the University of Michigan (attribution used with permission). In response to the query about RhIG effectiveness, to John's knowledge, there are no data to show that it will not be effective. John mentions an interesting paper by Lubenko A, et al entitled 'Should anti-Rh immunoglobulin be given to D variant women?' Brit J Haematol 1989;72:429-33. The investigators looked at the ability of partial D RBCs to adsorb anti-D from RhIG preparations. Except for one DVI sample, there was no appreciable reduction in anti-D titers; and with that DVI sample the titer reductions observed after 3-6 adsorptions could not be reduced by further adsorptions. Based on these in vitro data, the authors surmise that the amount of free anti-D (not bound to the partial D RBCs) would be sufficient to suppress Rh alloimmunization.
   
   In reply to the question about surveying opinions of women who are weak D, the answer appears to be no, unless other colleagues have data to the contrary.

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