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Rh typing in tube-when to call patient Rh positive


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Hello everyone!

 

We employ tube testing as our primary testing method.  I am new to my organization and have been told by the staff that the previous supervisor verbally stated that a reaction of 2+ or greater was required when testing with Anti-D in order to call a patient Rh positive.  However, the SOP states 1+ or greater.  I should also mention that the truth table in the Blood Bank information system for Rh testing is built to match the SOP.

 

My question to all is this:  if the 2+ or greater is indeed required to classify a patient as Rh positive, what is the reference?  I do not see this specific grading requirement in the manufacturer's insert nor do I see in the AABB technical manual.

 

Any help is greatly appreciated!

 

Thank you!

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what does the ani-D package insert say as to the interpretation of results?  Even if the pt is Weak D positive only we still called them Rh Positive.  There is some controversy with Rh rxs in gel - but I have never heard of such when tube testing is performed.

Edited by David Saikin
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what does the ani-D package insert say as to the interpretation of results?  Even if the pt is Weak D positive only we still called them Rh Positive.  There is some controversy with Rh rxs in gel - but I have never heard of such when tube testing is performed.

Precisely!  Read, read, read the package insert and make your policies based on the facts.  Not all Anti-D reagents are the same ... some detect weak D at IS, some after 37oC incubation, some require AHG Phase.  Furthermore, some are designed to NOT detect DVI (e.g. MTS). 

1. Does anyone know where the 'magic' number (grade 1+) came from?  Do patients with less than 2+ reaction make Anti-D even though they have the D antigen on their cells?  I suspect, like some of our 'old rules', there is nothing to support the statement ... especially knowing what we know now about making reagents and the D antigen.

2. Do ALL your techs perform tube testing to get the EXACT same results EVERY time?  Wow!  (Even the old titer QC allows a 1 tube deviation because humans are 'variable'.)

 

We follow the package inserts:  A positive result means the antigen is present = Rh Pos. (The Anti-D reagents we use do/don't detect DVI as appropriate for the reason for the testing, e.g. patients who are DVI, are to be classified as Rh Neg.  So, we can tell the difference.

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Precisely!  Read, read, read the package insert and make your policies based on the facts.  Not all Anti-D reagents are the same ... some 

We follow the package inserts:  A positive result means the antigen is present = Rh Pos. (The Anti-D reagents we use do/don't detect DVI as appropriate for the reason for the testing, e.g. patients who are DVI, are to be classified as Rh Neg.  So, we can tell the difference.

 

There are other D-varients that would give a low titre, as well as partial-D and mosaicism - to assume they are all D+ (bar VI) is wrong.

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1. Does anyone know where the 'magic' number (grade 1+) came from?  Do patients with less than 2+ reaction make Anti-D even though they have the D antigen on their cells?  I suspect, like some of our 'old rules', there is nothing to support the statement ... especially knowing what we know now about making reagents and the D antigen.

 

http://www.ncbi.nlm.nih.gov/pubmed/18067505  Here's one recent study.

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Well, isn't this timely. Apparently there is an article in this month's Transfusion about this very thing. Just received this memo today from a blood center.

I totally agree with everything that they say in the memo. But....who is going to pay for all of this molecular typing? And what about turn around time? hmmmmm....the plot thickens.

Weak D genotyping memo NY Blood Center.pdf

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Well, isn't this timely. Apparently there is an article in this month's Transfusion about this very thing. Just received this memo today from a blood center.

I totally agree with everything that they say in the memo. But....who is going to pay for all of this molecular typing? And what about turn around time? hmmmmm....the plot thickens.

 

I'm kind of right there with you. There's compelling arguments for the moneysavings for healthcare as a whole and there's definitely benefit for those annoying circumstances where between different visits or between other hospitals/laboratories there are discrepant RH results and the physicians immediately assume that our results are "bad."

 

I actually wrote a process document that matches what the NY Blood Center recommends for my institution. The medical directors of transfusion services and maternal/child health both approved, but we're still not live while we get the charges established, figure out exactly how this will work in the IS-world, and how to make this as user-friendly to the bench-staff as possible.

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Well anything that is neither clearly pos or neg (prefereably tested with 2 different anti-Ds at least) should have further testing.  But if time doesn't allow, err on the side of negative for a patient and you can't go wrong (unless the patient is a 90 year old man and never likely to have a transfusion again)

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We've been following a policy like this for performing Rh types for several years. It affects only a small number of our patient population. We have just started sending some specimens out for molecular testing as recommended by our blood center. Our medical director hasn't yet decided how he wants to deal with that information. At this point we are calling everybody that fits into the <2+ category Rh neg and recommending RhoGAM for those OB patients. That may change as he gets more comfortable with the molecular results and when there is a clearer consensus in the blood banking committee about how to deal with these types of patients (i.e. basing transfusion and RhoGAM recommendations strictly on the molecular report).

 

The AABB publication below discusses Rh types for Prenatal patients in detail - it was developed by W John Judd for the AABB Scientific Section Committee and he has written extensively about Rh types over the years. The 2+ 'thing' is something he recommends.

053065DB Guidelines for Prenatal and Perinatal Immunohematology
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My "dilemma" is that I don't use tube testing, we use the Tango (solid phase) as our primary method. So any D that is 2+ in tube testing is 3-4+ on the Tango. Which would mean sending every specimen out for molecular??? Or repeating all patients in tube testing to see if they are below a 2+ in tube? We're pretty high volume here, just trying to figure out how to accomplish this.

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My "dilemma" is that I don't use tube testing, we use the Tango (solid phase) as our primary method. So any D that is 2+ in tube testing is 3-4+ on the Tango. Which would mean sending every specimen out for molecular??? Or repeating all patients in tube testing to see if they are below a 2+ in tube? We're pretty high volume here, just trying to figure out how to accomplish this.

 

The article I posted references <2+ for tube and <3+ for column agglutination technique. I'm sure there have to be similar studies for Echo/solid phase. I vaguely recall reading one from the Canadian blood services. If I can find it I'll post a link.

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Interesting, thanks!

Somewhere there's an article that states that DVI is the 'weak D' that makes Anti-D, the other 'weak D' types don't. 

Dear JPCroke

no, that's not right, I'm sorry.  Most partial Ds and many weak D types have been documented as making anti-D; DVI is just the one most likely to do so amongst Europeans.

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Interesting, thanks!

Somewhere there's an article that states that DVI is the 'weak D' that makes Anti-D, the other 'weak D' types don't. 

 

 

Dear JPCroke

no, that's not right, I'm sorry.  Most partial Ds and many weak D types have been documented as making anti-D; DVI is just the one most likely to do so amongst Europeans.

 

As Anna said :) But you also need to take into account partial-D and moscaicism.

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If we get weakly reactive Ds on the Echo, we repeat the type by tube using the anti-D reagents from the Echo and the monoclonal blend we normally use for tube typing. If any of those 3 results is <2+, we call it Rh negative. These are the patients we consider for molecular typing. Thankfully it's not a large number of patients.

Edited by AMcCord
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  • 3 weeks later...

Dear JPCroke

no, that's not right, I'm sorry.  Most partial Ds and many weak D types have been documented as making anti-D; DVI is just the one most likely to do so amongst Europeans.

Thanks for this discussion! Yeah, I have also heard some people teach that only those with partial D can make an anti-D, not the weak D. Which weak D types have been documented could make anti-D just as Anna said?

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  • 2 weeks later...

We currently use Quotient anti-D.  It contains potentiators which makes it more likely to react (albeit weakly) with mostly type 1 or Type 2 weak D cells.  We can check them with the Immucor anti-D and it is negative.  Both are positive at IAT.  These same patients will test positive, sometimes 3-4+, in gel (which our other hospitals use for routine testing).  When we automate we will also likely use gel blood types.  U of Mich first published using a cut off of 2+ in MTS gel for calling a patient Rh positive (can't ever remember if it was equal to or less than 2+).  I don't know of anything published in tube testing.  We have been more cautious lately and calling our weaker reacting patients Rh neg, especially young females, because we had some that made anti-D.  We are trying to get a reasonable approach to this figured out that is faster than sending them for molecular testing and works on all of our testing platforms.  We could just go back to Immucor anti-D but our gel results aren't going to agree with it.  I look forward to seeing how Grifols' gel testing looks with some of these patients. 

 

I'll say it again, we just need a quick, clear cut test that tells us who can make anti-D.  I don't care what antigen they have or don't have!

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I'll say it again, we just need a quick, clear cut test that tells us who can make anti-D.  I don't care what antigen they have or don't have!

 

Well Mabel, if anyone ever comes up with that test, then they will make a fortune.  Unfortunately, it doesn't exist - and I doubt if it ever will.....

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  • 2 weeks later...

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