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Emelie

Patients with blood type A Bel, what to transfuse?

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Hi! We have a patient who genotyped as A Bel. Is the Bel subgroup a complete antigen or partial? The patient expresses extremely low levels of B, would it be safe to transfuse with AB blood? The patient has no detectable anti-B occurring naturally. As far as I can tell by the litterature, Bel cells are not agglutinated with anti-B (but do bind to them)?

We will, of course, have our doctor decide what recommendations to give, but I would like to know how other treat these patients as it´s a first for us.

Please explain it like I´m five :) 

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Putting aside the A antigen for the moment, which is probably "normal" in the case of your patient, it is not the B antigen that is abnormal in the case of a Bel person, but the 3-alpha-galactosyltransferase enzyme (the direct gene product of the ABO gene) is less active than normal, due to a mutation in the gene.  The actual carbohydrate residue that is on the red cell is "normal" - just less of it.  In addition, there is competition between the "A-transferase" and the "B-transferase" for the H-backbone.  In the case of your patient, the "A-transferase" will "win" this competition and this will accentuate the weakening of the B antigen even further - but the actual structure of the B antigen will be the same as the normal B antigen - just fewer in number.  This explains why there is no anti-B present in your patient's circulation.

This (rather long-winded) explanation should serve to prevent you worrying about giving your patient group AB blood should they require a transfusion.

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Thank you! I found it difficult to find general recommendations regarding Bel. I discussed it with our reference lab just now, they weren't convinced about the transferase's ability to produce a complete antigen, since the expression was extremely low. I thought, as you say, that the absence of anti-B would implicate a normal B antigen but they were unwilling to recommend anything but A or 0 blood. This particular patient has a mutation not earlier documented, so it might be their cause for taking extra caution. Thank you for some great insight! It's an amazing forum for gaining new knowledge!

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52 minutes ago, Emelie said:

Thank you! I found it difficult to find general recommendations regarding Bel. I discussed it with our reference lab just now, they weren't convinced about the transferase's ability to produce a complete antigen, since the expression was extremely low. I thought, as you say, that the absence of anti-B would implicate a normal B antigen but they were unwilling to recommend anything but A or 0 blood. This particular patient has a mutation not earlier documented, so it might be their cause for taking extra caution. Thank you for some great insight! It's an amazing forum for gaining new knowledge!

I don't want to interfere, but have you thought about sending a sample to Martin Olsson's laboratory in Lund?  He is the world authority on the ABO gene.

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It's Martin who's analyzed it (we've sent new samples so they can confirm their findings) ;) We'd better do as they say, then 😄

Edited by Emelie

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