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Antoinette Willis

RHoGAM work up post partum Weak D

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We currently run a week D on our post postpartum OB patients RHoGAM evaluation  in addition to our Fetal Screen. This test is being questioned as unnecessary. I would like some opinions and alternate

suggestions why we should or should not do the Week D

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22 hours ago, R1R2 said:

PERHAPS weak D was included because a positive weak D would alert you to a possible false positive fetal screen.  

That is what I always thought.  We dropped it when we went to our new computer system in August UNLESS the fetal screen comes up positive.  That hasn't happened yet.

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On ‎12‎/‎6‎/‎2018 at 10:16 AM, R1R2 said:

PERHAPS weak D was included because a positive weak D would alert you to a possible false positive fetal screen.  

It is a good reminder to generalists who can forget over the years that a strongly positive fetal screen with a negative Fetal stain is not a weird result (?!?) - it is probably just a weak D.  Without doing weak Ds regularly, it is easy to forget that as the years pass.  Doing the weak Ds as part of the RhIg workup is a different idea.  We just do them once on any Rh Neg and put it in the computer history.  I am trying to catch the young females and send them out for genotyping - nice to have a definitive answer that gives assurance of the right choices for individual pts.  So far, we have sent our genotyping to the UBS Reference Lab - which sends them on the Grifols Lab.  We get them back in about 2 weeks, so it goes in computer history for the next time we see the pt. 

Has anyone been using Immucor's Lab for RH genotyping?  How long do they take and how much do they charge?  (if anyone knows)

 

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Weak D if fetal screen is strongly Positive out of curiosity or to explain results but this + result would still require a fetal stain.  We would place a comment in the patient's file to alert future pregnancies of need of fetal stain for RHIG coverage.

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On ‎12‎/‎10‎/‎2018 at 8:32 AM, AMcCord said:

We would do weak D on a post-partum patient only if the fetal screen is strongly positive.

Then still follow up with a Fetal Stain?  On all future pregnancies also??

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Yes, a Kleihauer-Betke would be performed plus we would indicate in the patient record that Kleihauer-Betke is required for all future deliveries if the patient is weak D positive. We would not repeat the weak D testing.

And as a side note, if the patient's baby was weak D positive, Kleihauer-Betke testing would be performed.

Edited by AMcCord

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We used to do weak D tests with post-partum RhIG workups because we did a full blood type and antibody screen with them to make sure mom was a candidate.  (Also, to look for massive FMH that would cause an Rh neg mom to look like a weak D but that was before the Fetal Screen/rosette test was invented.)  In those days, weak D pos moms were not RhIG candidates, but they are now.  With modern reagents, those who react only at AHG anti-D testing are likely to be partial D VI and more likely to make an anti-D.  We would rather not find them and just call them Rh negative from the IS test so we don't do weak D testing routinely on obstetric patients.  We all dropped the antibody screen when we started using sensitive techniques like gel that picked up the 28 week RhIG dose at the time of delivery.  If the screen was negative, you gave RhIG; if the screen was positive with anti-D (unless it was super strong) you still gave RhIG so why do the test if it won't change the treatment?  Now we do weak D tests only if the Fetal Screen is "diffusely positive" to understand if a weak D is causing it.  We get surprisingly few of them.  Of course we do weak D tests on the babies of Rh neg moms.

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On ‎12‎/‎14‎/‎2018 at 9:02 AM, ANORRIS said:

Then still follow up with a Fetal Stain?  On all future pregnancies also??

 

Edited by ANORRIS

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I think the terms "strongly positive" or "diffusely positive" do not accurately describe the results of an immune resetting test on a Weak D positive blood sample.  By definition, the test is routinely read with a microscope.  An unexpected result is macroscopic agglutination and this is what we see with a Weak D positive and D positive blood samples.

Our procedure states that if macroscopic agglutination is observed in the immune resetting test, then a Weak D test is indicated for that blood sample.

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16 hours ago, Dansket said:

I think the terms "strongly positive" or "diffusely positive" do not accurately describe the results of an immune resetting test on a Weak D positive blood sample.  By definition, the test is routinely read with a microscope.  An unexpected result is macroscopic agglutination and this is what we see with a Weak D positive and D positive blood samples.

Our procedure states that if macroscopic agglutination is observed in the immune resetting test, then a Weak D test is indicated for that blood sample.

There is no such thing as "Weak D positive", on the grounds that there is no such thing as "anti-Weak D".  There is, however, a myriad of different Weak D types.

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Correct, there is no such thing as "anti-Weak D", but the Weak D test is done and it is interpreted as either "positive or negative" (assuming a negative control test).

Procedurally, if a Weak D test on a blood sample (that gave a macroscopically positive immune resetting test) is also agglutinated (usually =>2+) , I will interpret that test result as a "positive Weak D test" or "Weak D positive" and report the patient to be Rh Positive.

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