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a,b positive in O baby with a Mum anti-D quant of 847IU

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Hi Everyone, 

We did an IUT on a baby yesterday whose Mum has an anti-D quant of 847IU. Baby's pre-transfusion sample we tested on the Biovue card and the result was neg with the anti-A and anti-B but 4+ with the A,B. The D and the control well and DAT are also 4+. Any idea why the a,b is reacting with these cells? 




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The DAT is easily explained, with an anti-D level that high!  Even after a double exchange transfusion, there will still be approximately 5% of foetal/neonatal red cells in the circulation, which is quite sufficient to give a positive DAT, but with an IUT, you are not removing an foetal red cells from the circulation (or minimal amounts) and should be considered more as a simple top-up transfusion (with profuse apologies to people who work in the Fetal Medicine Units, as I fully realise that there is nothing remotely "simple" about an IUT).

As far as the reactions with the anti-A,B, the anti-D and the control is concerned, while the anti-A and anti-B are negative, it must be remembered that there are potentiators in monoclonal antibodies, such as albumin, that will possibly lead to them giving "false positive" reactions (although, I would suggest, that the reaction with the anti-D is anything but false - unless the anti-D is blocking the D antigen sites, which, with an anti-D level of 847IUmL-1 [it is NOT 847IU, which is an amount, rather than a concentration] would not be in the realms of impossibility).  The amount of potentiator in each specificity will be different, depending upon what the antibodies are designed to detect (for example, what A and B subgroups, if any).  However, the anti-D will most certainly contain potentiators, to ensure that most weak, and some partial D types are detected.  This means that the control, which will have the same make up as the anti-D reagent - but without the anti-D, in other words, it would contain potentiators that would detect "false positives", which is the whole point of the control.

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