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Loss of B Antigen


Gkloc

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We have a patient who starting getting transfusions every 2 weeks starting in Oct 2014.  Patient is AB Negative and every unit transfused has been A Negative except one which was O Negative given in Dec 2014.  The patient came back for another transfusion last week and when performing her ABO/Rh type the results were:

A: 4+

B: 0

D: 0

A cells: 0

B cells: 0

Control: 0

 

We incubated the B for 15 mins and 30 mins at room temperature and got a very weak reaction when doing that.  Patient diagnosis is Thymoma and pure red cell aplasia and is being treated with cyclosporin.  Patient has not received a bone marrow transplant.  I have found some information in journals about this but nothing really definative.  Has anyone else come across something like this, or know how or why this can happen.  Thanks for any help you guys can give.

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There are (at least) two answers to this - and there may be many more for all I know.

Firstly, ABO antigens can be affected by the genes that govern them if the mutation that causes the underlying pathology is close on the same chromosome to the genes encoding the genes that encode for the transferase enzymes that govern ABO antigenicity (NOT the best piece of English grammar I have ever posted!!!!!!), and, as a result ABO antigens can be weakened. However, one would have expected a weakening of the A antigen under these circumstances, to accompany the weakening of the B antigen.

Secondly, of course, it could be that the original finding of AB was actually a case of group A who had an acquired B antigen. Normally, of course, there would also be an anti-B present, but, if the patient also was immunosuppressed, this would not always be detected. It could be that the patient is now a straightforward group A, with no infection (hence, no acquired B antigen), but also no anti-B, as the patient is still immunosuppressed; she/he is on cyclosporin.

Then, of course, it could be that the first samples were taken from the wrong patient (but this would also mean that this was done multiple times, probably by the same phlebotomist, who thought that they KNEW the patient, but I doubt this!

And now over to others for more realistic answers!!!!!!

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You stated the patient has red cell aplasia.  Your findings would be consistent with total and complete red cell aplasia and the only circulating cells are transfused donor units, which you stated were all A's. The amount and frequency of transfusion would also be consistent with the total aplasia.   

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I agree with Goodchild and SMW.  We had an AB Pos patient who developed a new antibody every time we transfused her until she ran out of ones to develop.  There was no way our blood suplier could find AB units for her, so she always got type O and never again typed as AB.  Additionally, many of her antibodies ceased to be detectable, and when she moved, we stressed to her the importance of giving her new transfusion facility her blood type card with all her antibodies listed.  Surprise, surprise, the new facility typed her as O Pos, even though she had no reverse reactions.

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BankerGirl, we've noticed this quite frequently with newborn babies who have had repeated IUTs at a Specialist Fetal Medicine Unit, and have then gone back to the original referring hospital and we, as the Reference Laboratory, have been told nothing of this history, and then get a complaint from both hospitals (and our own Quality Department) because "we don't know how to do ABO typing"!

 

Frustrating???????????????????!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

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Malcolm, we have a premie born in Oct.2014 who was originally A positive, but due to number of O positive red cell transfusions (top-up) now types as O positive. I have a question:  Should we continue to transfuse O positive red cells even after baby completes 4 months age or change to the original A group as the neonatal period comes to an end?

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I would change to A Positive, as long as there is no transfused anti-A in the circulation.

 

ABO antigens are histoantigens, and so a) most, if not all of the transfused anti-A will probably be adsorbed onto the tissues, and B) as the A antigen will be expressed on the tissues, the baby's immune system should not recognise the A antigen as non-self.

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