A Weak D Dilemma

[jhaig]

We had a patient come in yesterday who recently moved up from Virginia who said she had always been told she was RH-negative. We perform weak D testing on any female of child-bearing age, and wouldn't you know that she was a 2+ weak D positive. SO...we called her RH-positive, weak D variant and notified her doctor's office that she was not a candidate for Rhogam. Needless to say, this caused mass confusion. The patient has three children and received Rhogam in the past.

My guess is that either a) she's never had a weak D test performed on her or her previous care givers just called her Rh-negative and gave her Rhogam as a precaution so as to not confuse her about her blood type.

Then I check the AABB standards and find standard 5.20.2 which (paraphrasing) implies that a patient shall be considered for Rhogam if the woman's test for D antigen is negative, but a test for weak D is not required.

Who out there does routine weak D testing on females of child-bearing age? Has the weak D become obsolete or have I gone insane?

[donellda]

We only do weak D testing on Rh negative babies born to Rh negative mothers. I think that the current line of thinking is that a mom could still form anti-D even if she is a weak D variant so we stopped doing the weak D test on moms and now just focus on the babies.

[Gerald]

We only do Weak-D testing on Rh negative babies with Rh neg mothers for the same reasons as "donellda".

[rcurrie]

Weak D testing is obsolete if you are using it to determine RHIG status or blood recipient status. The problem is that weak D positive patients MAY be able to make anti-D (to the portion of the D antigen they don't make), and weak D positive moms can still make anti-D. So, to make things simple, toss that weak D test unless, like me, you are testing donors. Everyone else is Rh negative and an RHIG candidate if a mom.

BC

[Mabel Adams]

But, this is a fairly recent change so you are not insane and I am sure you are not alone. We just quit doing weak D on moms in the past year.

[jhaig]

In order to drop the weak D, I need to find the information on where and when these changes took place. I have the CAP standard, but can't find where AABB recommended this change.

[John C. Staley]

There was a recent AABB teleconference presented by John Judd on this very subject. You should be able to get a copy of the slides and a CD from AABB. That should get you on the right track.

We still weak D test every D neg patient. I have discovered that inertia is the single most powerful force in human nature. Trying to over come it in our organization is an impossible task. This is one battle I have given up on.

[Mabel Adams]

AABB publishes a booklet called Perinatal Guidelines that contains an excellent explanation of the policy and the justification for it. (John Judd wrote it.)

[kate murphy]

I'm with the majority - weak D only on cord bloods and donors. Actually, once you get the data to back you up, the techs really like it - streamlining testing. The docs don't even notice. The only doc you need to convince in your med director.

One caveat if you draw auto donors - weak D testing on donor and not on the patient sample could give discordant results. If you do donors, think about how you'd address that.

[conwaysbb]

If you go to www.aabb.org website, in the Technical Questions and Answers link of the Member's Area you will see this question and answer that pertains to your post:

When is it Necessary to Perform a Test for Weak D?

Q: As the medical director of a 200-bed community hospital, I am responsible for review and approval of policies and procedures, including those for the blood bank. We have no SBBs on staff, but our blood bank section leader has come to me with a request to stop performing Du tests. She also says the term Du is considered obsolete, and has been replaced with “weak D.” What is the proper terminology and when, if ever, should a blood bank laboratory perform the test for weak D?

A: Yes, terminology has changed. Many terms have been used to describe Du, leading to confusion for blood bankers and clinicians. Particularly confusing are the terms D-negative, Du -positive and Rh-negative, Du -positive. In 1984, in an attempt to avoid such confusion, Moore1 proposed use of the term “weak D. ”This proposal later was supported by Agre et al.2 Subsequently, “weak D” has replaced “Du” in most scientific and regulatory publications. Characteristically, weak D red cells are nonreactive with anti-D reagents in direct agglutination tests, but do react with IgG anti-D based reagents by the indirect antiglobulin technique.

As the terminology has changed, so has the formulation of anti-D typing reagents. Samples that once were classified as weak D, using reagents prepared from human IgG anti-D, may now react directly with reagents formulated with monoclonal IgM anti-D, some of which are blended with either human or monoclonal IgG anti-D. Considerable data on the molecular biology of human blood groups also have been gathered, increasing our understanding of weak D.

Weakened expression of D is the result of missense mutations or gene rearrangements (hybrid genes containing sequences derived from both RHD and RHCE). Missense mutations encoding the transmembrane portion of the D protein manifest as weak D, which often is associated with a low antigen site density. Most carriers of these weak D alleles are not prone to D alloimmunization. Further, their red cells should type as Rh positive in direct tests with reagents formulated with high-affinity monoclonal IgM anti-D.3

Hybrid genes and missense mutations encoding portions of the D antigen that are external to the red cell membrane account for partial D phenotypes, some of which also present as weak D. Individuals of a partial D phenotype are at risk of making antibody to the portions of D that are absent from their red cells.3

Thus, for the purpose of pretransfusion testing and identifying women at risk of D alloimmunization from pregnancy, it is desirable that partial D individuals be typed as Rh-negative. In this regard, current anti-D reagents do not react directly with red cells of the most common form of partial D, DVI.

In response to the second part of the question, it is worth looking at the situations in which tests for the D antigen are performed, to determine the relevance of testing for weak D.

Donor testing , by the collection agency, prior to Rh-type labeling—For allogeneic donors, testing for weak D is required since weak D red cells can evoke production of anti-D in D-negative recipients.

Confirmatory testing of units labeled Rh-negative, to identify a significant labeling error—Here the purpose is to look for gross labeling errors. The test for weak D is not required.

Pretransfusion testing, to determine if Rh-positive or Rh-negative donor red cells and/or platelets should be selected for transfusion—Given that partial D individuals can make anti-D if transfused with normal D-positive red cells, they should not receive D-positive blood. Therefore it seems prudent not to test potential transfusion recipients for weak expression of D.

Pregnancy , to decide if the woman is at risk for alloimmunization to D and, if so, to identify them as candidates for Rh immune globulin (RhIG) therapy—Testing for weak D in pregnancy is not required. Partial D women can be considered candidates for RhIG therapy both during pregnancy and after delivery. There are no data showing that RhIG therapy will not be effective.4

If an anti-D based method (rosette test, flow cytometry) is used to evaluate for excessive fetal-maternal hemorrhage (FMH) at delivery, a “false-positive” test may occur if the mother is of a weak or partial D phenotype.The required dose(s) of RhIG should be determined by a method that detects hemoglobin F in fetal Red Blood Cells (RBCs), such as the Kleihauer- Betke test.

Infants of women at risk for alloimmunization to D, to verify that the mother is a candidate for postpartum RhIG therapy— The “standard of care” is to test for weak D. If the test for weak D is positive, the mother is a candidate for RhIG therapy. However, a “false-negative” result likely will be obtained if an anti-D based method is used to evaluate the degree of FMH, due to the low D antigen site density of the fetal red cells. The required dose(s) of RhIG should be determined by a method that detects hemoglobin F in fetal RBCs.4

References:

Moore BPL. Does knowledge of Du status serve a useful purpose? Vox Sang 1984;46(S):95-7.

Agre PC, Davies DM, Issitt PD, et al.A proposal to standardize terminology for weak D antigen. Transfusion 2002;86-7.

Flegel WA ,Wagner F. Molecular biology of partial D and weak D: implications for blood bank practice. Clin Lab 2002;45:53-59.

Judd WJ. Practice guidelines for prenatal and perinatal immunohematology revisited. Transfusion 2001;41:1445-52

By E. Ann Steiner, MT(ASCP)SBB, Ortho Clinical Diagnostics, Raritan, N.J. and W. John Judd, FIBMS, MIBiol, University of Michigan, Ann Arbor, Mich.

Hope this points you in the right direction.

[Eagle Eye]

We have Gel Technology. We perform retype from same specimen if patient doesn't have prior record. One typing is done by traditional tube method and one is done by manual gel technique.

If we decide to drop weak D testing, we will run into same as problem as Autos. Our patient will type as RH positive by gel(as gel is more sensitive) and patient will type as RH neg with Direct Antiglobulin test. Right now if patient is weak D we do not get discreoancy with gel and tube method.

It doesn't make sense in using GEL to retype the patient...it will be an expensive option.

:confused:

[geekay]

Hi there !

As far as the procedure you have adopted, it is theoretically right.. No confusions required here.

Regarding the terminology, "Du test /Du antigen " have been replaced with the word

"weak - D antigen." since the past 10 years or so.

Simple practicality of the situation is , if the "weak D test " could not be reported within the time limit of 72 hours, go ahead with giving Rhogam , assuming that it is Rh POSITIVE.

After all, there is no damage done ..right ?

[geekay]

Hi,

Not only that the "gel technique" is expensive, but many incidents have taught me that the "gel technique" gives false positives frequently.

Maybe more inputs from the other readers would be appreciated in this context.

I have found in so many situations that, false aggregations and rouleaux formations do give "positivity" in gel technique.

More inputs please !

After all they say, when there is confusion, go by the old gold manual technique. !

[rcurrie]

The number one goal is to protect the patient. So, you can never go wrong calling a patient Rh negative with that goal in mind. However, if you call a patient with less than optimal reactivity with anti-D Rh positive, you could invoke sensitization to the D antigen if you transfuse Rh positive blood. So, to protect your patients, give all patient Rh typings to the tech with the hardest shakedown. ;-)

Just be glad if you don't do donor testing also! If you do, my advice is simple: donor testing techs are donor testing techs; transfusion services techs are transfusion services techs; never the twain shall meet.

BC

[geekay]

Blood banking is an art of "playing safe"..thats what they say...!

Two things are entirely different !

One : To give Rhogam or not : If the "Rh Positivity" could not be detected within 72 hours, then proceed as if it is "Rh Positive" and give Rhogam ! So no damage done !

Two : Regarding "transfusion requiremnt" : if required as an SOS, go ahead and give Rh Negative Blood . Whats so confusing here ?

Three : Regarding reporting : For newborn, sometimes when there is a borderline situation of calling it as Rh negative or Rh Positive, a repeat sample after 3 months is suggested as protocol in some of the accepted Books.

[jhaig]

I hereby claim victory in my battle to eliminate weak-D testing at my institution. I presented all of my research to pathology last week. My pathologist notified me today that we don't need to do any weak-D testing on pre-natal or pre-transfusion testing any more. He said it seemed superfluous and, for the amount of Rhogam we give out annually, a few extra vials would have little to no impact. Thanks to all of you that helped me in this quest.

I've dropped weak-D testing on auto donor units as well. I don't want to have different results on the patient sample and their auto unit - the less confusion the better. Since we don't cross over auto units (if they don't get transfused back to the patient, they get tossed), it shouldn't be a problem.

[geekay]

Hi there !

Is it a real solution to the problem or an escapism ?

You are solving the problem by giving Rhogam...agreed ...

But are you going to call the patient / donor "positive" , "negative" or "weak D positive" ?

In this modern era of increasing awareness, if a literate patient or a donor asks for a report ?

Different hospitals/institutions following different protocols in matters like this, will lead to confusion only ?

[jhaig]

If protecting a patient equals 'escapism', then yes, my solution is escapism.

My whole problem arose from a patient that had been previously typed at another hospital as Rh-negative. When she came to our facility, we performed a weak-D and found her to be weak-D positive. So, by our protocol, she was reported as Rh-Positive, weak-D variant. Well, she was extremely confused by our report. My guess is that the previous facility that tested her never did a weak-D and, for convenience and her safety's sake, just called her Rh-negative and was done with it.

Through my research and consultations with regulatory agencies, as well as the great info found from my fellow blood bankers on this site, I've determined weak-D testing to be obsolete and it does not benefit the patient to do them anymore. I actually created more confusion for this patient by DOING a weak-D, so by eliminating weak-D testing we've streamlined the whole process and made things easier all around without affecting patient safety one bit.

If a well-informed and enlightened patient wants a report, they'll get a report saying they're Rh-negative. They won't know the difference unless they have been told before that they were Rh-positive. As the trend seems to be that more and more facilities are eliminating this test, this should be less and less of a problem. And it's not like we're giving them incorrect information or trying to 'trick' them, either. They would get accurate information based on our testing protocols. Personally, I wouldn't care less about my blood type unless my care, or especially my child's care, would be adversely affected.

[dcross]

As I work for a transfusion service and we only test donors, we call the weakest Ds (including Del) D positive. We often get indignant calls from donors insisting that they are D negative.

I completely understand the thinking in omitting the Du test in the hospital but maybe the report should refelect the fact that the patient was not etsted for Weak D so that at least it makes more sense when you are trying to explain the discrepancy to them.

[rcurrie]

I never have any trouble explaining the discrepancy. I have donors who are also patients, so it happens enough for me to be quite good at it. I simply say, "Mr. Smith, as a donor you are Rh positive because you make at least a portion of the D antigen, which is called the Rh antigen. Your blood could cause a recipient to make the anti-D antibody. But, as a patient you are Rh negative because you could make anti-D should you receive Rh positive blood. You could possibly make this red-cell destructive antibody even though you make a portion of the D antigen." I have never had this explanation questioned. I only run into this problem with one in 10,000 donations. However, if I were to tell all donors their weak D status, I would be on the phone continuously explaining this. So, no, we don't explain weak D up front when giving donors or patients their blood types.

BC

[dcross]

Sorry, you misunderstood me. I didn't mean to tell donors (or patients) that they were D weak. Rather, if the D is not tested by IAT (i.e. Du test), maybe for D negative patients should have a statement like "Weak D antigen has not been excluded" on their reports.

Your explanation to the donors is very good though.

DC

[galvania]

I've been reading this thread with interest. In Europe the situation is generally that patients are tested with two different anti-D reagents. Both should be IgM and at least one of them must not react with DVI. On no account is a weak D test (Coombs) to be carried out. Patients who are positive with both anti-D reagents are considered as D+ and transfused with D+ blood, even if both reagents give weak positive results. Most labs work with gel, and this means that all but the weakest of weak Ds will react as positive. If one anti-D is pos and the other neg, then the patient is treated as a probable Partial D and treated as a D-. Donors are also tested with 2 anti-D reagents. At least 1 of these must react positively with DVI. Many centres continue to do a Coombs D on the negatives; others use an anti-CDE reagent as a surrogate marker for D antigens that are otherwise undetectable using routine techniques.

I have a couple of specific questions.

1..To jhaig - is it possible that your patient was not in fact a weak D but had a positive DAT? You did not say whether you had put up an auto control at the time of testing and I don't know what the practise is in the States. In Europe anyone testing a Coombs D should alsop put up a control.

2..for aakupaku. I was very suprised to see that you have some cases of D antigens that are coming up positive by gel and negative by Coombs. I have been working for 16 years with gel technology and have never seen such a case - but then that's doing everything in gel and using monoclonal reagents. I can see that it is possible if using polyclonal reagents in the gel with enzymes in the cell diluent.

3..for engeekay 2003. You said that you found many examples of false positives in gel, especially with rouleaux. Again I find this puzzling unless you are using polyclonals with enzymes. In my experience, I have less problems with rouleaux in gel than I ever did in tubes. If you have time, details would be nice to satisfy my curiosity

[jhaig]

I must have left that detail out. The patient did, in fact, have a negative DAT in gel and in tube. I thought of that as well. Thanks for helping me think!:cool:

[AMcCord]

A poll question for those of you who have dropped routine weak D testing: What reagent are you using for routine D typing (does it react with DVI or not, etc)? and Do you use the same reagent for weak D testing of babies? Just curious.

[Mabel Adams]

We use Gammaclone anti-D on everyone.