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Do you have a weak D policy when tested on the Provue?


Johnv

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We started using the Provue in 2013.  Currently when testing prenatal and maternal patients to determine if a patient is a candidate for RhIg immune globulin or Rhogam, we perform tube and weak D testing.  Considering the AABB Std that weak D testing is not required, we looked at dropping it all together (except cords and neonatal testing),  The Provue ABD gel card package insert says it will detect nearly all forms of D antigen so we are considering using the Provue result exclusively.  A quick survey of other labs with Provues in our area shows most are still using weak D testing to various degrees.  If you use a Provue, did you drop weak D testing?  Or do you only perform weak D if there is a +1 or +2 reaction in gel as some facilities are doing? thanks.    

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We don't do Weak D testing on adults, only newborns.  Doing Weak D testing on specimens yielding 1-2+ on ProVue routinely produces the same strength of reactivity in the Weak D test as in the Immed-spin D test, i.e., 1-2+. We do Weak D testing on Provue using ORTHO BioClone Anti-D.  We interpret these test results (1-2+) as Rh Positive.  We don't do any D/Weak D testing in tube.

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We have the Provue set up to not transmit the result when the D is 1+ or 2+.  At that point we do it in tube to see if it is negative.  If the tube is negative, we will report out negative.  The Provue states that it can catch nearly all weak D, but what about partial D's?  It was the thought of our pathology team that since partial D patients will present sometimes as weak D, it would be best to perform the test in tube and call it negative if it comes up negative in tube to be sure that the patient receives Rhogam.  Albeit, literature does state that a partial D person has a minimal chance of producing anti-D to the parts that they do not possess, we have had 2 cases here thus far and they have really given the doctor's a headache.  Hence the reason for this process.  Since we do reference work, I must field the weak D question at least monthly.  We seem to be having a lot of problems with discrepant results depending on the platform used to test the anti-D between us and other area reference labs.  I have had to explain to many of them that our policy err's on the side of caution.

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Are you referring to this article by Dr. Judd and others?   

 

Rh discrepancies caused by variable reactivity of partial and weak D types with different serologic techniques
  1. Gregory A. Denomme,
  2. Louann R. Dake,
  3. Daniel Vilensky,
  4. Lily Ramyar,
  5. W. John Judd

Article first published online: 7 DEC 2007

DOI: 10.1111/j.1537-2995.2007.01551.x

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Are you referring to this article by Dr. Judd and others?   

 

Rh discrepancies caused by variable reactivity of partial and weak D types with different serologic techniques
  1. Gregory A. Denomme,
  2. Louann R. Dake,
  3. Daniel Vilensky,
  4. Lily Ramyar,
  5. W. John Judd

Article first published online: 7 DEC 2007

DOI: 10.1111/j.1537-2995.2007.01551.x

 

 

That's a good article. I think it's the right one.

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  • 3 weeks later...

We have a Provue and do not do weak D testing on prenatal specimens or active labor patients.  If we have a 1+ or 2+ result on a D reagent well it is reviewed but is reported as Rh positive.

 

You could follow these up with weak D testing in tube but remember, it's 2 different anti-D reagents and I bet you would get a weak D positive result anyway.  I have found that the D reagent in the ABD/Reverse card is more 'sensitive' than the Ortho tube reagents.

 

We only do weak D testing in on patients as David stated above.  

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We do not perform Weak D testing on Prenatal Samples so not a ProVue issue for us. We only do that testing on Cord Specimens (which we do manually).

Brenda Hutson

We started using the Provue in 2013.  Currently when testing prenatal and maternal patients to determine if a patient is a candidate for RhIg immune globulin or Rhogam, we perform tube and weak D testing.  Considering the AABB Std that weak D testing is not required, we looked at dropping it all together (except cords and neonatal testing),  The Provue ABD gel card package insert says it will detect nearly all forms of D antigen so we are considering using the Provue result exclusively.  A quick survey of other labs with Provues in our area shows most are still using weak D testing to various degrees.  If you use a Provue, did you drop weak D testing?  Or do you only perform weak D if there is a +1 or +2 reaction in gel as some facilities are doing? thanks.

 
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  • 3 weeks later...

We have a Provue and do not do weak D testing on prenatal specimens or active labor patients.  If we have a 1+ or 2+ result on a D reagent well it is reviewed but is reported as Rh positive.

 

You could follow these up with weak D testing in tube but remember, it's 2 different anti-D reagents and I bet you would get a weak D positive result anyway.  I have found that the D reagent in the ABD/Reverse card is more 'sensitive' than the Ortho tube reagents.

 

We only do weak D testing in on patients as David stated above.  

 

I have a question about reporting 1+ or 2+ Rh reactions on the Provue as Rh positive.  

 

Page 4 of the 2005 AABB “Guidelines for Prenatal and Perinatal Immunohematology” states:    "Only when prenatal tests for Rh are unequivocal and clearly reactive (=/>2+) should the woman be considered Rh-positive.”

 

Dr. Joe Chaffin, The Blood Bank Guy, also states a similar opinion in his excellent podcast "Weak in the D's".  Here is a link to his podcast:

 

http://www.bbguy.org/podcast/1012/1012podcast.asp

 

The podcast is 41 minutes long, and if you don't have 41 minutes, skip to 34.12 minutes into the podcast.  That's where he starts talking about OB patients.  At 35.30 minutes into the podcast, he says that transfusion services should consider a lower threshold of positivity for calling Rh negatives--some places call a 1+ reaction or lower in tube testing Rh negative and a 2+ reaction or lower in gel testing Rh negative.  The risk here is giving Rh negative blood when Rh positive blood can be given, but calling these weak Rh reactions Rh negative lowers the risk of immunizing the patient.

 

I am interested in this because last week I realized I didn't have a weak D policy, except that we only perform weak D testing on cord bloods if the mom and baby test Rh negative. 

 

Last week we reported an OB patient as Rh negative, using tube testing with Ortho anti-D bioclone.  The patient's physician informed us that the patient was determined to be Rh positive 2 years ago when the patient had her first child.  I called the lab that performed that testing and found it was a 1+ reaction on the Echo Galileo.  The lab reported that the patient was “Rh Positive by Weak-D test (formerly Du).  RhoGam is not indicated for this patient”.  

 

We use the Ortho MTS gel cards for ABO/Rh testing (manual method) as well as tube testing with Ortho reagents, so we repeated the patient's testing using the gel method, and saw a 1+ reaction for the Rh.  When we performed the tube weak D test, we also saw a 1+ reaction. 

 

(An aside--we are a small lab, performing about 100 type and screens per month, about 40 crossmatches per month, 10 cord bloods per month.  I have been trying to phase the MTS ABD Reverse cards out.  The tube method is more versatile, it is faster in emergencies and according to a cost analysis I did, the tube method is ½ the price of the gel ABO/Rh method.  However, the lab is staffed with generalists, and I have been told it’s better for generalists to use the gel method—no chance of forgetting to add the reagent and more consistency.  We perform antibody screens using the gel method because it is more sensitive (although I realize the gel antibody screen method has its pitfalls such as being a LISS method and possibly missing anti-E and anti-K sometimes, etc.)

 

Anyway, I have come to realize that I need to write a weak-D policy, and I am thinking of including these points: 

  1. Perform weak D testing only on cord bloods when mom and baby are Rh negative, on Rh negative moms when the FMH screen suggests the mom may be weak D positive, and when investigating discrepancies such as the OB patient last week.
  2. Calling Rh results less than 2+ in gel and less than 1+ in tube, Rh negative.
  3. When the Rh results are less than 2+ in gel and less than 1+ in tube, reporting the Rh as negative and including a comment that indicates the Rh type is weak and atypical and if the patient is a blood donor, the patient would be considered Rh positive, but if the patient is an OB patient or a recipient, the patient should be considered Rh negative.

There is a CBBS posting about when the AABB changed the weak D regulations in 2002.  Dr. Judd is quoted as saying that, when it was decided in 2002 that weak D testing was no longer needed to be performed on OB patients, all of a sudden, patients that had been D positive, were suddenly D negative, and this was in the same facility.  Dr. Judd is quoted as saying that these patients were informed of their options...that is, where previously they were D positive and did not require RhIG, they were now D negative, and they could opt to receive RhIG or not...they needed to sign a form.......I hope I remember that correctly....

 

I would like opinions!

 

Thank you!

 

Catherine

Edited by cbaldwin
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As I work in a Reference Laboratory, I have access to allsorts of anti-D reagents and, if necessary, can send out to the International Blood Group Reference Laboratory for molecular work, so people may not think that I am qualified to comment on this. However, I DID use to work in several hospital Blood Bank laboratories, and I think you protocol sounds just fine Catherine.

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We really need to go back to the drawing board on our terminology for weak D.  We have patients that react weakly at IS with anti-D and those who react only in the "weak D" test (AHG) so which do we mean when we say "weak D"?  We can't work them all up for partial vs. weak D type 1 and type 2 so we need some more logical way to refer to them.  AHG-dependent D???  Of course that depends on the antiserum being used.  Malcolm, don't you have pull with bigwigs who could start over with naming this beast?

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We are just beginning to approach this subject here too -

 

For several reasons we have been slow to change -

1.  Complex policy difficult for generalists to remember over time - easy to miss one that "should have been done"

2.  Hard to remember why a Fetal screeen may be "very" positive when they no longer remember much about Rh neg (weak D positive).

3.  We are in a region that doesn't have an abundant supply of Rh negative units anyway - tough to justify using them on a Rh pos Weak D when a real Rh neg might need them desperately.  We had a looooong period of A neg shortages this year during the flu season.

 

I do realize that the reagent themselves have changed over time, but the real change for us has been going to solid phase testing on the ECHO.  Weak Ds all come out 4+ positive anyway.  In tubes that may be a 2-3+ positive, sometimes weaker, but not on solid phase.

 

I am thinking about keeping the weak D testing the same, but changing the Interpretation of the ABORh results from Rh Pos to Rh negative in my computer system.  That way, we don't forget what Weak D is all about, we know the reactivity of the pt's blood type and can expect the problems on Fetal Screens (or skip them all together on these pts and go straight to Fetal Stains).  We wouldn't have to remember to do the Weak D testing only on Rh neg babaies of Rh neg moms - sure to be forgotten once or twice! 

 

We are going to have a meeting soon with the OB docs - they will be the ones most affected by the change - and ask them what they want to do.  I'm not sure about asking the pts what they want to do (from an earlier post) but I can see we are going to have to ask the Drs what they want to do when it comes to RhIg administration to the few pts that convert from Rh pos now to Rh neg in the future.  Canned comments would be good - I liked some of the wording on that earlier post too.

 

Some may feel this is a waste of testing - but it isn't very many pts anymore anyway and I would just rather "know" about these pts up front anyway.  Anybody else feel the same way?

 

Also - even though the reagent manufacturers are trying real hard - do the Anti-D reagents still react with the occasional true Partial D with a strong positive reaction?  I thought I understood that to still be the case.  These are the pts you really wish would come out a clean Rh neg.  Oh well - never a perfect world.

 

I would love to hear from anyone still in the same position as us.

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1.  Complex policy difficult for generalists to remember over time - easy to miss one that "should have been done"

2.  Hard to remember why a Fetal screen may be "very" positive when they no longer remember much about Rh neg (weak D positive).

 

I can relate to the above comments.  Everyone in my lab is a generalist.  They work hard and do their best but it's easy to forget.  I didn't understand weak and partial D until recently.  (I think I understand now!)

 

Fortunately we are small and there are not many of us so I can contact everyone with a weak-D policy in-service/mini-lecture.  

 

Some may feel this is a waste of testing - but it isn't very many pts anymore anyway and I would just rather "know" about these pts up front anyway.

 

I would rather know about these patients too...

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Um, are you absolutely and utterly certain that you now understand Weak and Partial D cbaldwin?

It used to be that, if the mutation in the gene resulted in an amino acid substitution only intracellular and/or the intramembranous part of the red cell (or more than one), but not one that was extracellular, then it was Weak D, as the immune system would not recognise a "wild-type" D+ as "foreign".

If the mutation resulted in an amino acid substitution (or more than one) that was extracellular, plus or minus one (or more than one) that was intracellular and/or intramembranous, then it was a partial D, as the immune system would recognise a "wild-type" D+, a Weak D or a Partial D of another type, as "foreign".

Sadly, since we have now found alloanti-D, albeit incredibly rarely, in Weak D Type 1, 2 and 3 individuals, this no longer holds true.

So, if you do understand Weak and Partial D, please explain the difference to Geoff Daniels and me (amongst others)!

ONLY JOSHING. PLEASE DO NOT TAKE OFFENCE!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

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  • 1 year later...

We only do weak D on infants when the mother is Rh negative, and on mothers when an FMH is strongly positive. Most of our positive FMH (which are subsequently reported out as inconclusive) are in mothers with a positive weak D

I too am looking at dropping the weak D test.  So you report the fetal screen as inconclusive, do you perform a KB stain?  Do you still give RHIG?  How do you determine dose of RHIG?  Thanks!

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Yes, you have to do a KB stain to determine RhoGAM doseage in those cases. We give one vial of RhoGAM to those moms (if the baby is Rh positive) with a comment that "KB is pending - additional doses of RhoGAM may be indicated".

 

When we have the KB results: if negative - we report that with the comment that patient has received one vial RhoGAM , no additional vials recommended; if positive - we report that with the comment that patient has received one vial RhoGAM and X additional vials RhoGAM are recommended.

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