D Typing Dilemma

[Dawn]

Lately we have had quite a few weak D positive patients who have made anti-D. We have begun to question our policies regarding patients who are weak D positive.

Here is where we stand:

· If there is any reactivity with anti-D in any phase we consider the patient to be Rh Pos and we transfuse Rh Pos. We generally do not give RhIg to Rh Pos patients, including weak D positive patients.

· Currently we perform weak D testing only for babies and donors (and in a few other odd situations).

· We are considering using the weakest anti-D reagent that we can find. That way we will call most weak D positive patients Rh Negative. The weak anti-D should still be able to pick up weak D at AHG.

I have heard that some institutions have a cut-off based on reaction strength. For example if the reaction with anti-D is 1+ or weaker they report the result as Rh Negative.

I have also heard that some institutions seek to identify pregnant patients who are category DVI. Patients in this category of partial D seem to be more apt to produce anti-D if exposed.

I’d love to hear from those of you who are also caught up in this dilemma. Please give details.

[David Saikin]

I am assuming you are talking about historicac weak D pts, as you state that you only do weak D on babies and donors (usually). Our protocol matches yours for weak D, however, I am certain that the volume of pts I test pales next to yours (we do about 350 tx/yr), and we have yet to see any anti-D's, except for one historical pt (type VI). I do not have any solution to your problem but do commiserate with you. I do not like calling those 1+ D's Rh neg, after all they obviously have the D antigen. They can always be give Rh neg red cells.

[conwaysbb]

In years past, I too have had the policy of interpreting patients whose weak D test was <2+ as Rh Negative. (interpreted as Du pos, Rh Neg) However, at that time the facility did not have a computer system. This analog could not be used in a computer system, because truth tables could not be set up to accept this.

At our institution, we do not perform weak D testing on specimens, except for donor testing and cord bloods of babies whose mother is Rh Negative (heel sticks if cord is not received). The only reason to do weak D on cord bloods is so that if Weak D test is positive the mother's specimen is not tested for the fetal screen but goes directly to Hematology for a Klein Becky test.

As for using the weakest anti-D reagent, I would not do this as the monoclonal anti-Ds that are out there are all not the same (I am assuming you are using the monoclonals). Depending on which one you use, there should be some product limitations listed which would define which partial Ds it takes or not detects. I would also talk to your reagent manufacturer about your concerns.

[adiescast]

We also only do the weak D test on cord bloods from Rh negative mothers and women with obstetric diagnoses (we don't collect donors). We give Rh negative blood to people who are Rh negative at immediate spin. This avoids the whole question of giving Rh positive blood to weak D positive recipients (although it does cause higher use of Rh negative products!)

[Myella]

We have the same policy that ConwaySBB had in the years past. We still currently perform Du testing on all patients and our cut off is <2+ to call it Rh neg. We also have Hemocare computer system. I haven't encountered this situation since we went live with Hemocare. Although, I think it will be printed out in the exception report.

[Kochman]

There is an on-going discussion on the CBBS web-site too. See:

http://www.cbbsweb.org/enf/rh_testing_dvi.html