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Anti M


CSP0102

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I would like to know how people handle Anti-M when they find it at IAT phase.  Do you give antigen negative blood or prewarm it away and consider it not significant?  Also if you have patient history of the Anti-M showing at IAT phase and the next time you do a workup it doesn't show how do you handle it.  Significant or not?

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I use gel which predisposes for anti-M reactivity. When I find one I perform a strict pre-warmed screen using homozygous and heterozygous cells. If I find reactivity at AHG (using anti-IgG) then I go with antigen negative rbcs/no reactivity I will transfuse ahgxm compatible (prewarmed technique). In my reference experience I have seen folks transfuse M+ rbcs with no adverse reactions. In these instances I have found anti-M that only reacts with homozygous M cells (in gel)and I tell the referral not to be concerned. Sometimes the Medical Director of the referral will call and want M= rbcs; they are usually satisfied if a prewarmed is negative.

If I am not finding a pre-existing anti-M I am not concerned.

I always like to hear what Malcolm has to say on this (or any) topic.

Edited by David Saikin
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At our hospital we use solid phase and we do find Anit-M here and there.  If  Anti-M is demonstrating at 37 or AHG, we will antigen type and AHG crossmatch units.  If there is previous history of -M and it is not demonstrating, we will AHG crossmatch units but not antigen type for M.  And finally if it is only demostrating at IS, we will prewarm away.

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Thank you for your kind comment David.

 

Anti-M is the bane of my life!

 

Until relatively recently, if an anti-M was referred to my laboratory, we would test it first by Bio-Rad (Used to be Dia-Med) gel IAT and enzyme technique (enzyme technique to see if anything else is there - even I know that the M antigen is destroyed by papain!!!!!!!!!) to make sure that there was an anti-M present.  If there was an anti-M present, we would then test it by pre-warmed, warm-washed LISS tube IAT at 37oC.  If we saw no reactions by this technique, we would advise that cross-match compatible blood would be suitable, and safe, for transfusion.  If we did see reactions by this technique, we would advise that M- typed blood should be cross-matched, and those compatible transfused.

 

The reason for the difference between the gel technique and the tube technique is two-fold.

 

Firstly, in the gel technique, the reactants (plasma and red cells) are introduced to each other at room temperature, and then the cassettes are put into a 37oC incubator.  "Cold-reactive" antibodies can sensitise red cells in "peco-seconds" (I may have exaggerated a bit there!!!!!!!!!!!), but the antibody-antigen complex takes a bit of time to dissociate (longer than the incubation time), and so a "false IAT positive reaction" is seen.  On the other hand, if the reactants are introduced to each other, already at 37oC, "cold-reacting" anti-M will (eventually) sensitise red cells, but not in the time allowed for incubation, and so the reaction would be negative.

 

The second reason is that the column containing the AHG is slightly acidic, and if there is one antibody/antigen reaction that likes acidic reactions, it is that between anti-M and the M antigen.

 

I was quite happy with this situation, BUT, and my own line manager is well aware of this, so I don't mind saying it publically, NHSBT has decided, on the grounds that most of our hospitals use gel techniques, we now recommend giving M- typed blood to anyone who has an anti-M, which I think is a total waste of units of blood that have been typed for all sorts of other antigens and have been found to have (presumed) homozygous expression for other, more useful, antigens.

 

I am well aware of the fact that anti-M can cause haemolytic transfusion reactions (IF serologically reactive at 37oC) and can cause clinically significant haemolytic disease of the foetus and newborn (IF serologically reactive at 37oC), and, in the case of HDFN, particularly amongst ethnicities in the Far East, such as the Japanese, irrespective of titre, but these cases are very, very rare.

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Thanks for the information. I still would like to know if you have given M - units in the past when the M showed at Coombs phase what do you do when it doesn't show in future testing? We have 2 different view points in my Blood Bank. Once significant always significant or if it's not there don't worry about it

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I do not treat anti-M as "once significant, always significant".

 

Logic says, for one thing, that at least a proportion of those we detect that DO NOT react by pre-warmed, warm-washed LISS tube IAT at 37oC, the first time WE see them, must have worked by this technique before we saw them.  We have given cross-match compatible, but not M antigen negative blood to loads of such people, and NONE have undergone a transfusion reaction.

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I would worry a little about that mprado.

 

Although a clinically significant anti-M is a rare bird, it does exist.  Geoff Daniels quotes examples that have cause immediate and delayed haemolytic transfusion reactions, and goes on to say that, "The suggestion that anti-M and -N can have haemolytic activity was supported by the results of 51Cr survival studies and monocyte phagocytosis assays."

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I use gel which predisposes for anti-M reactivity. When I find one I perform a strict pre-warmed screen using homozygous and heterozygous cells. If I find reactivity at AHG (using anti-IgG) then I go with antigen negative rbcs/no reactivity I will transfuse ahgxm compatible (prewarmed technique). In my reference experience I have seen folks transfuse M+ rbcs with no adverse reactions. In these instances I have found anti-M that only reacts with homozygous M cells (in gel)and I tell the referral not to be concerned. Sometimes the Medical Director of the referral will call and want M= rbcs; they are usually satisfied if a prewarmed is negative.

If I am not finding a pre-existing anti-M I am not concerned.

I always like to hear what Malcolm has to say on this (or any) topic.

Ditto!

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So, when you prove the anti-M doesn't react by the pre-warmed technique (which in our hands would be a saline technique) do you then crossmatch the units by gel (uses less sample, sensitive to other antibodies to low frequency antigens) or by pre-warmed technique (longer incubation but more likely to find compatible units)?  I am thinking particularly of those that show dosage and react in gel only with double dose cells.  Our computer won't allow electronic xm if we have ever turned out a positive Ab Screen, even if it was insignificant.  Do some of you do E-XM in the presence of an insignificant anti-M?

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If a patient has been identified with an Anti-M using Gel technique we retest at 37 to see if it prewarms away. If it does prewarm away, we give AHG crossmatch compatible units. If the M is prewarm positive, we give M negative, AHG compatible units.

 

We do honor the history of the antibody by AHG crossmatch compatible units regardless if it is reactive at 37 or not or even if it doesn't show up in subsequent antibody screens. We treat Lewis antibodies the same way. And like "mprodo" we advise to use a blood warmer if it is a strong M.

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So, when you prove the anti-M doesn't react by the pre-warmed technique (which in our hands would be a saline technique) do you then crossmatch the units by gel (uses less sample, sensitive to other antibodies to low frequency antigens) or by pre-warmed technique (longer incubation but more likely to find compatible units)?  I am thinking particularly of those that show dosage and react in gel only with double dose cells.  Our computer won't allow electronic xm if we have ever turned out a positive Ab Screen, even if it was insignificant.  Do some of you do E-XM in the presence of an insignificant anti-M?

Our computer is set to NOT allow eXM if the current antibody screen is positive even if antibody is not significant (ABSC test of record is Gel).  For historical antibodies and current Gel ABSC neg eXM is allowed if antibody is not clinically significant.  We have anti-M set as not cignificant.  We would do extended AHG XM anytime the ABSC is positive due to anit-M and we use Gel plus Immed spin as our XM method for these.  If the anti-M is historical we would do eXM.  We do not antigen type units for current or historical anti-M.

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I agree with JoJo808. If it prewarms away we give crossmatch compatible. If it doesn't, then we screen. The computer may not like the anti M, but that's why I built the override code: "antigen screening not required." !

Liz

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