No adult Du testing.....what do we do with weak D moms?

[lab217]

Our policy is not to do Du testing on adults. When we get to the fetal bleedscreen, post delivery, the rare weak D (Du positive) moms are identified at this stage (very positive fetal bleedscreen and negative for fetal cells).

According to the AABB, these patients are not RHIG candidates.

These patients are called RH neg up until this point and have been given RHIG.

How do other facilities handle these situations? Any information would be greatly appreciated.

[tbostock]

There has been some recent discussion about this in other threads. Many seem to be encountering this, due to different methodologies (gel, solid phase, tube testing) in use. Do a search for weak D on this forum and read the responses, and then you should discuss with your Medical Director how to handle these cases at your facility.

[Liz]

What is a fetal bleedscreen ? And I am not sure I understand what you are asking. Moms that are weak D may form anti-D if baby is D positive. So we consider them D negative and they are given RHIG, thats what you said, so what is the question?

ok I read your post again. AABB says that they are not candidates for RHIG. Hmmm i must check that. In reality if they are mosaic they may form anti D so they should recieve rhig unless you want to check molecularly. But better to be even more cautious than AABB if that is written and what is your concern? you wont get cited write your internal SOP on this. I hope i got you right.

Dont forget to tell me what you mean by a fetal bleedscreen.

[lab217]

I am sorry, i will clarify. Immucor offers a kit that is called the fetal bleed screen test (FBS). It detects RH positive rbcs. We do this test on all delivered RH antigen negative moms with a baby that is RH Positive. If the FBS is negative we only give on unit of RHIG. If the FBS is positive we then must do the Kleihauer Betke (KB) to determine how many units of RHIG is appropriate. The problem becomes weak D moms. They have very positive FBS results and negative KB results. In order to be sure that this is a weak D situation and not tech or some other error, we must do the weak D test. At this point we "know" the patient is a weak D and the AABB technical (seventeenth edition) manual states that these women are not RHIG candidates "clearly positive on the weak D test should be considered D positive and not receive RHIG, although rarely a positive weak D test can be caused by a partial D antigen". This statement from the AABB technical manual is confusing.

We do not do weak D testing on adults, including prenatal moms. But we "catch them while doing the FBS. This ca

[EDibble]

Liz, if it is like our own, the fetal screen is a test performed on a post partum , Rh negative mom's blood to screen for the presence of Rh pos cells. This is done when the baby is Rh pos of course. If the screen is positive, the quantative Kleihauer-betke is done. (I wish we had flow cytometry!)

[Liz]

Thank you for the clarification. I dont have that test, maybe i should. We perform the KBT.

Regarding the AABB statement: "... rarely a positive weak D test can be caused by a partial D antigen": this is key to the whole wording. It means that it may not be weak but partial and the mom may thus get alloimmunised. So give RHIG and lets ask them at the meeting. the way i see it this last statement confuses the first part of not giving rhig and seems to be what one may call a disclaimer... ""we told that it may be partial so be careful". this leaves the decision up to you. I do beleive we should give rhig.

Thank you, interesting.I shall look up the test too. Is it a requirement?

[Liz]

Flow.. ah yes, but the doctors give one dose without the KBTest so as not to charge more on the patient, if we performed flow they would certainly object.

I am going to look into this test by Immucor, thanks.

[Mabel Adams]

The fetal screen test is a rosette test for detection of D pos cells in the mom's circulation. I think the Tech Manual needs to be updated. It seems like the modern monoclonal anti-D reagents are specifically designed to only detect category VI partial D at AHG so I think that a lot of the strong reactions we would pick up in the weak D test could be partial D's and therefore should get RhIG.

[R1R2]

The fetal screen test is a rosette test for detection of D pos cells in the mom's circulation. I think the Tech Manual needs to be updated. It seems like the modern monoclonal anti-D reagents are specifically designed to only detect category VI partial D at AHG so I think that a lot of the strong reactions we would pick up in the weak D test could be partial D's and therefore should get RhIG.

I agree with Mable. We recommend RHIG unless we know, by molecular testing, that patient is a weak D.

[Mabel Adams]

And I have two weak D patients, one a type 1 and the other a type 2 by molecular testing that have made anti-D. Only one is young enough for child-bearing, fortunately.

[David Saikin]

We count them as Rh= and they get RhIg. Have to do K-B to determine if a fetomaternal hemmorhage has taken place.

[marvy1]

We debated this issue back and forth. Decided to go the more conservative route and consider these "Weak-D" moms eligible for Rhig since a percentage of these "Weak-D" moms are actually partial D capable of forming Anti-D or are those uncommon "Weak-D" that also can form Anti-D

[Dr. Pepper]

We debated this issue back and forth. Decided to go the more conservative route and consider these "Weak-D" moms eligible for Rhig since a percentage of these "Weak-D" moms are actually partial D capable of forming Anti-D or are those uncommon "Weak-D" that also can form Anti-D

Ditto for us with the moms, and with transfusion candidates as well (give them D neg). Many years ago we had a patient who had an ambiguous D typing but a nice positive weak D test. We gave him D pos blood per AABB recommendations and sent him on his way. No problem until he went to have elective sugery some months later and his new anti-D made him incompatible with a half dozen directed-donor relatives. Didn't go over very well.

[rravkin@aol.com]

I had a case once where the mother typed as Rh- Pos but historicaly, from her doctor's office, typed Rh-Neg. She was currently delivering and had RHIG administered as part of her pre-natal work. She was currently Rh typed by myself and another tech at another time and with another specimen, and the Rh typing we generated was confirmed. After delivery the patient's doc continued with RHIG administration for this patient despite the Rh-Pos result obtained. I couldn't blame the doc for continuing with the RHIG given possible future litigation and the already high cost of malpractice insurance. The doses of RHIG the patient received pose no threat to her or baby's health; and as an interesting side note, when typing the patient's specimen for Rh you could see how the agglutinates were not as crisp and well defined as usual. They looked almost like visible fat globules in the aqueous solution which gave us a deeper understanding of how water is excreted upon the formation of the agglutinate such that clear and crisp agglutinates are generated. During the formation of agglutinates for this patient's rbc's water could not be fully excreted because the RHIG blocked bonding of the Anti-D, from the reagent used, to D antigen on the patient rbc's and therefore could not expell all of the water as the agglutinate formed giving raise to it's awkward macroscopic appearence. The water would have actually been trapped within the latus frame of the agglutinate.

I would have to agree with the practice of erroring on the side of caution as our bench methods for determining Rh type do not differentiate between a weakly expressed D antigen or an altered or mosaic D antigen.

As far as molecular testing is concerned; if the testing determines a weakly expressed D antigen will this knowledge ensure that the patient's immune system not generate an allo-D antibody? Is it a known fact that a patient's immune system will not generate an antibody against a auto antigen that is correctly structured but weakly express?

Edited October 3, 2012 by rravkin@aol.com