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Cliff

Rh Pos or Rh Neg?

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OK, not Rh, but D.

We were using solid phase technology and recently switched to gel (IH-1000).

We've had a policy for many years, if you test less than 2+, we call you Rh Neg.

Now with gel, people who were 1+ are testing 2 or 3+.

This is concerning for OB patients.  Do we give Rh immune globulin or not?  We've sent a few of these out for genetic testing to determine if they are capable of forming an anti-D, but if they've just delivered an Rh pos baby, and we don't get the results back for weeks, it's too late.

We are a big organization and have a very active labor unit.  We used to do about 10 thousand babies a year, but lost a big contract and now do less than 8, so there are significant financial impacts to our decisions, and since our volume is so high, we also risk finding that patient that tests as 3+, but can make an anti-D.

What are you doing?

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  With Gel, we test anyone who is 2+ or less. Most of our weak D's come up 2+. If they haven't had genetic testing, we give them RhoGam to be safe.

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At our facility if the patient has an Anti-D of 2+ or less we consider the patient Rh Negative and issue RhIg. The sample is then sent to the reference lab to determine if the patient is a weak D or partial D by molecular testing.

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If it's positive in gel, we consider them positive. It's been that way at this facility since we went to gel in 2004. We haven't see any complications because of it, but then with our volumes we probably wouldn't. Probably the majority of our daily testing is prenatal type and screen testing from our doctors office. We don't have a huge daily volume though. A dozen separate patients would be about as busy as we'd get. I would say most of our patients are pretty healthy with strong antigen expression. I don't see many below 2+ on them. We only weak D test cord bloods.

Isn't it the general statistic that 16% of Rh neg mothers will develop anti-D without RhIgG? You can probably run the numbers on how many you have that test at 1+ and 2+ and then check their results against any DNA testing you've done. You might find that the low the percentage may not be worth the extra fuss. I believe I heard the number of people having just one child is increasing. Huge world of statistics to consider!

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Dr John Judd - an expert on gel and many, many other blood bank topics - recommended calling patients Rh positive if they reacted 3-4+ and any patient reacting 2+ or less Rh negative. He had stats from many, many patient samples and if I recall correctly, he was involved with beta testing for gel. I believe this Rh study was published in Transfusion (late 90's?). Maybe someone here can put their finger on that reference. There are newer articles out there that also support this. Your Ortho tech rep should be able to provide you with references.

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1 hour ago, AMcCord said:

Dr John Judd - an expert on gel and many, many other blood bank topics - recommended calling patients Rh positive if they reacted 3-4+ and any patient reacting 2+ or less Rh negative. He had stats from many, many patient samples and if I recall correctly, he was involved with beta testing for gel. I believe this Rh study was published in Transfusion (late 90's?). Maybe someone here can put their finger on that reference. There are newer articles out there that also support this. Your Ortho tech rep should be able to provide you with references.

Is it Denomme GA, Dake LR, Vilensky D, Ramyar L, Judd WJ.  Rh discrepancies caused by variable reactivity of partial and weak D types with different serological techniques.  Transfusion 2007; 48 (3): 473-478?  I have to admit that I haven't read it yet (not least because I have forgotten my AABB password!).

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4 hours ago, Darren said:

Do people call antibody screens negative if they are 1+ or 2+?

I call them weakly-reactive, while antibody screens that are 3+ to 4+ are termed strongly-reactive.  Either way, they are documented in the computer as "Positive".  In my experience (20+ years with gel), the majority of positive antibody screens detected in gel were weakly-reactive.

As trained observers, we expect to see strong agglutination (3+ or 4+) when performing Rh(D) typing with anti-D reagent antisera.  Weak agglutination (<3+) is unexpected and should be investigated.  Judd's paper provided statistical evidence for interpreting weakly-reactive test results with gel anti-D

ORTHO's current IFU (version 3.0) classifies any positive test result (regardless of strength) with gel anti-D as Rh Positive (assuming a negative control test).  Judd's paper is not cited in the IFU's Bibliography.

Interpreting weakly-reactive test results with gel anti-D as 'Rh Negative' contradicts ORTHO's FDA approved IFU.

Edited by Dansket
update with additional information

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15 hours ago, Darren said:

Do people call antibody screens negative if they are 1+ or 2+?

An EXCELLENT question Darren ! I look forward to some interesting debate.

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I suppose if you are dealing with a cold-M (with positive reactions in gel) that you later successfully warm-away with tube testing, you could consider the antibody screen negative, when technically you would have a positive gel screen to begin with.  But this is not the same as reporting a "positive" screen as negative!

Scott 

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On 10/11/2018 at 10:25 AM, Malcolm Needs said:

Is it Denomme GA, Dake LR, Vilensky D, Ramyar L, Judd WJ.  Rh discrepancies caused by variable reactivity of partial and weak D types with different serological techniques.  Transfusion 2007; 48 (3): 473-478?  I have to admit that I haven't read it yet (not least because I have forgotten my AABB password!).

Excellent, and thank you.  Very helpful.

Here was my takeaway:

Therefore, we recommend that samples yielding
an IS tube test cutoff score of not more than 5 (i.e., ≤1+
hemagglutination) or a score of not more than 8 (i.e.≤2+
hemagglutination) by gel technology, be considered D–
for the purpose of transfusion and Rh immune globulin
prophylaxis.

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It was a bit of a troll question. It seemed to me that if we can't trust the reactions we get in gel then what's the point of using it. As far as I can tell regarding the IFU's Dansket is right.

I realize the importance of precision and care being taken in the blood bank, but I think a lot of times we fall victim to an overabundance of undue caution.

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So, a pregnant woman tests 1+ pos with anti-D.  Do you give her RhIg?  She has many (MANY) Rh pos cells of her own, will the RhIg simply attach to those cells.  What if she tests 2+?  What if she previously tested 0 (prior method for us was solid phase (or tube)) and now tests 3+, do you change her type?  Do you give her RhIg now because you used to call her Rh neg even though now you call her Rh Pos?  What if you didn't have a prior type on her, you'd only know her as Rh pos.  What do you tell the docs when you gave her RhIg at 28 weeks when she tested 1+, but now tests 3+ and you call her Rh pos and don't recomend RhIg?

We are having more and more trouble, no idea why this seems "new" to us.  We currently have a pregnant woman who tested 4+ with anti-D in gel and has a history (at another facility) and anti-D and anti-E.

The more we talk about this the more confused we (I) get.

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I would have got her RHD gene sequenced earlier in her pregnancy, so that I would have a better idea as to whether she required anti-D immunoglobulin.

If she turned out to be (potentially) a Partial D, or a Weak D other than Types 1, 2 or 3, I would give a double dose of the normal dose of anti-D.  Anti-D immunoglobulin is still derived from humans, which means it is a "soup" of different anti-D specificities against the 36 odd epitopes, some of which would be expressed on the lady's red cells, and some of which would not.  Therefore, some of the anti-D specificities would be adsorbed onto the lady's own red cells, but others would remain in her plasma, and would be "available" to react with the red cells of her foetus's red cells, and so would give her some protection against producing her own immune anti-D.

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On 10/11/2018 at 9:25 AM, Malcolm Needs said:

Is it Denomme GA, Dake LR, Vilensky D, Ramyar L, Judd WJ.  Rh discrepancies caused by variable reactivity of partial and weak D types with different serological techniques.  Transfusion 2007; 48 (3): 473-478?  I have to admit that I haven't read it yet (not least because I have forgotten my AABB password!).

Hi Malcolm,

I think there is an earlier article as well, but this is a good one. Thanks.

And ...regarding your reply to Cliff about giving RhIg...you said to give the lady with Partial D or weak D (other than type 1, 2, or 3) a double dose of anti-D. That's new to me. Can you provide me with a reference for that? I want to discuss that idea with my medical director.

 

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