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Anomalous anti-D?


David Saikin

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Have an 82 yo female, O Neg GI bleed.  Presents with a pretty straightforward anti-D EXCEPT some bothersome negative cells.

Most cells, R1R1 and R2R2 are 2+ (gel).  One R1R1 is absolutely negative, one is very w+.  RzR1 is 1+.  All other clinically significant

antibodies have been ruled out.  What am I missing here?  Her auto is 1+ in gel, DAT in gel is negative.

thanks in advance

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Well David, I see your problem, but I may be able to suggest an answer.

Firstly, the anti-D seems to be quite weak (which is what made me think of my proposed answer).

Secondly, of the "common" Rh types, the R2R2 type has the highest number of D antigens per red cell (15 800 to 33 300), and so will tend to give stronger agglutination than will an R1R1 (which may explain why you are getting agglutination with all your R2R2 cells).

Thirdly, and turning to the R1R1 red cells, some of these may, of course, be R1r', rather than R1R1, and, therefore, have fewer D antigen sites per red cell (about 9 900 to 14 600, compared with 14 500 to 22 800) and, unless the donor is genotyped, or you can do an informative family study, you may never know (but remember the Cepellini effect).  In addition, the number of D antigen sites expressed on a "normal" R1R1 can vary quite a lot from one individual to another (and, indeed, from one cell to another, in the same individual).  In other words, those R1R1 red cells that react with your patient's anti-D could be near the "22 800" end of the spectrum, whilst those that do not react with this anti-D may be nearer to the "14 500" end of the spectrum.

All figures are taken from Geoff Daniels' book, Human Blood Groups.  3rd edition, 2013, Wiley-Blackwell, page 205.

I am not saying for one moment that this is the only, or the most logical explanation, but it is, at least, one explanation!

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4 hours ago, exlimey said:

Could be an (auto) anti-LW, not uncommon in older folks. DTT- or AET-treatment of the test cells might give some insight.

Could be - but much more likely to be a weak example of anti-D.  However David, if you have some group O. rr cord blood available............

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