weak D test

[Linda McWilliams]

What is your facility doing?

We are doing the weak D test on women of child bearing age / and only once.

fetalscreen is peformed when indicated

[Lcsmrz]

We perform weak D testing on all females <50 yo and all first-time Rh negs. Fetalscreens are done on problems >27 weeks.

[conwaysbb]

We changed our process in July of 2004 for weak D testing. We only perform Weak D testing on donors and cord bloods (or heel sticks if cord blood not available) of RH negative mothers.

We got approval for not performing weak D testing from our OB/GYN Director. The thought process was that even if mother was weak D positive, these individuals could still produce anti-D as these are most probably qualitatively different weak D patients. The new antisera's that we use today detect quantitatively different weak D patients as Immediate Spin D positive.

We test our donors for weak D which has caused some problems with our autologous donors who are D positive (weak D positive test)for the Autologous donation but , since we do not perform weak D test on our patients, is deemed Rh negative. to take care of this issue, we place a comment into our patient historical file that a weak D test is to be performed.

For our cord bloods we perform weak D testing only on cord bloods from babies of mothers that are Rh negative. This testing will both ensure that the mother gets Rh immune globulin if baby is weak D positive and also will require us to not perform the fetalscreen on mother but send the mother's specimen directly for a klein-becky test as the fetalscreen does not reliably detect weak-D fetal cells. Even if the mother is weak D positive and you give Rh immune globulin, the reaction if any would be sub-clinical (weakly reactive DAT).

I believe you can see more information about not performing the weak D test on the AABB site in Q&A

[johna]

I fully support the idea that the "weak D" test should be eliminated on prenatal patients. Unfortunately I'm coming from a national reference laboratory situation. Getting a hospital OB/GYN director to approve this is one thing. But I'm quite sure that no matter what type of physician education we might employ we would never get this concept accepted by 99% of the OB physicians nationwide.

[conwaysbb]

I fully support the idea that the "weak D" test should be eliminated on prenatal patients. Unfortunately I'm coming from a national reference laboratory situation. Getting a hospital OB/GYN director to approve this is one thing. But I'm quite sure that no matter what type of physician education we might employ we would never get this concept accepted by 99% of the OB physicians nationwide.

I don't see why not. You use different reference ranges for your chemistry and hematology tests than a hospital based hematology/chemistry would since your reference ranges are based on different demographic than a hospital's demographics. Physician's always question the differences between results from reference labs and hospital labs, but they do accept them when it is explained to them.The AABB Q&A for this subject has a good explanation for this change with references that could be used. The only problem would be your different RH results from some of the hospitals that would still use the weak D test.

You could also find articles about RH positive, Weak D positive patients that have made anti-D and I am sure the explanation that today's monspecific, polyspecifc clones anti-D's are much stronger than the human derived anti-Ds that were in use years ago and could not differentiate between weak Ds that were due to quantitative differences versus qualitative differences.

The best way would be to get ACOG to recomend this change or at least send out information explaining this.

[David Saikin]

Our OB docs were very amenable to this change. We gave them the new standard and the AAbb Q&A. The Medical staff made the change in procedure contingent on the approval of the OB's, as it would really only impact that group.

[johna]

The best way would be to get ACOG to recomend this change or at least send out information explaining this.

This is an excellent point. I think that working this through the ACOG would probably be the most effective means along with us directly contacting clients.

Unfortunately, my only experience with the ACOG was about five years ago when I wrote to offer a negative opinion on the reference to "albumin titers" in one of their bulletins. The only response I received was that my letter would be passed on to the committee. To this day the bulletin still refers to a critical albumin titer of >=16 and a critical antiglobulin titer of >=32.

In any case it's worth another letter. Thanks for the suggestion.

[kate murphy]

We just stopped doing weak D on women <50 - our new policy is only donors and cords of Rh Neg moms. Our OB's had no problem with that.

[donellda]

We started doing weak D's only on Rh negative babies born to Rh negative moms about 2 years ago. This is the only situation in which we do them.

[John C. Staley]

Despite all my heroic efforts we (our corporation) will continue performing wD testing on everyone. Sometimes reason and DATA do not prevail while inertia and fear of changes does. I probably should stop now before I get my self in more trouble.

[bbbirder]

This is interesting...

A few years ago when various BB gurus suggested that the weak-D test was not needed for most patients, I discussed it with our BB Medical Director. We agreed to drop it (except for cord bloods and our auto on initial testing). We sent a memo to the doctors to inform them of our change and we never heard another word from any of them about it.

(Sometimes involving others in decision making is not a good idea.)

Linda Frederick

Phelps County Regional Medical Center

[Mary]

I would be interested in learning what everyone thinks about the articles in the October 2005 issue of Transfusion about weak D and testing of prenatal and cord bloods with 2 different antisera, different methods, etc.Ann Steiner also has a presentation on this subject.

Mary

[bevydawn]

How does not testing OB patients for weak D affect how and when fetalscreens are done and the results? We routinely test all our OBs and cord bloods for weak D and the only reason we are still doing them on OBs is because the higher-ups feel that it would cause too many problems with the Fetal Screen.

[EdSandlin]

How does not testing OB patients for weak D affect how and when fetalscreens are done and the results? We routinely test all our OBs and cord bloods for weak D and the only reason we are still doing them on OBs is because the higher-ups feel that it would cause too many problems with the Fetal Screen.

There are two layers to the ansewr to this question:

1) Weak D positive mothers will cause fetal screen tests to be unreadable. The indicator cells attach to mom's cells instead of to fetal cells causing large, visible clumps rather than microscopic rosettes.

2) This doesn't matter because it is really obvious and you just have to cancel the test for that mother. Once in a blue moon you may waste time on an invalid test but this is far outweighed by weak D testing for ALL your D "neg" moms, which is shamefully wasteful of time and resources.

[labgirl153]

My facility performs weak D testing on cords only, but this was implemented only recently. It's been well received for the most part. Most everywhere I've worked in recent years has dropped the weak D testing with little or no negative comment.

The only problem encountered thus far was the case of a woman who had always been typed as weak D positive via reference lab and previous hospital stays, but now, as a result of the new protocol, she was typed as Rh negative. She had just delivered her sixth child (Rh pos like the previous five). The frustrated OB had us switch the type back to "weak D pos" because, he wasn't about to change her type after six deliveries and start her on Rhogam, when "she'd never needed it previously" (antibody screen is still negative).

Of course, she might have just gotten lucky all the previous times or perhaps she was group O and the babies all either group A or B, which would have allowed her immune system to swiftly destroy the A or B fetal rbcs before her immune system recognized the foreign D epitopes and responsed to it.