4 September 2017 (Monday) - Anti-M

Here’s a case study close to home… this happened to me in the middle of the night at the end of last week…

A patient presented just before midnight with low Hb and with a GI bleed. Male, in his seventies, and with no transfusion history. Units of blood were requested…

As there was no history I insisted on having two blood samples taken at different times. Cell groups presented as A Rh(D); however the reverse groups presented as O. Agglutination was seen in both A and B cells. Antibody screens in both samples were negative.
My immediate reaction was that this was a case of A2 with an anti A1. However with no anti A1 available I was unable to confirm this. But this theory went out the window when two of the four units of blood I crossmatched were clearly incompatible.

I did photograph the antibody panel; I wish I knew what I did with the picture. But suffice it to say the results were incredibly inconclusive. By now it was 3am and I was just a little bit worried.
I had another look at the antibody panel and realised something. Reactions had occurred in cells that were all homozygous for the M antigen. Anti-M would explain what was going on. But lacking any anti-M reagent I was unable to confirm the M-status of the supposedly compatible units. They could well have been heterozygous and test compatible but could cause a reaction.

I spoke to the doctors and explained the situation. I had two units which might be compatible, but I couldn’t be sure.
The patient was stable, and we arranged for further samples to be taken to be sent to the reference lab, and for M-negative units to be supplied from the NBS.

Now (a few days later) I’m told I did the right thing(s). But I can’t help but wonder where the anti-M came from… and what would I have done if they had insisted on transfusing him?

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