Clinically Significant Anti-M

[jch]

May sound like a dumb question but for patients with a clinically significant anti-M, which crossmatch method does most everyone prefer: gel or tube? Thanks

[tbostock]

Not a dumb question at all...either method is valid.  And it's really only clinically significant if it is causing hemolysis in the patient, which is extremely rare.  No need to screen units for M, just do AHG crossmatch in either method and select the compatible ones for transfusion.

[SMILLER]

By clinically significant do we assume you cannot get rid of it at 37 C or AHG no matter what method (gel, pre-warm, etc.) you use?  In which case you would have to use M neg units.

 

Otherwise, we have the least trouble with pre-warmed tube methods.  But they can be tedious.  It seems like we have the most trouble with gel with an otherwise insignificant anti-M.

 

Scott

[Malcolm Needs ☆]

There is good reason for that Scott.

 

Firstly, the reaction well at the top of the cassette will be at room temperature when you add your cells and palsma, and so a "cold" reacting anti-M will sensitise the red cells prior to the cassette being put into the 37^oC incubator, but the incubation time is insufficient for the anti-M to dissociate from the M antigen.

 

Secondly, even if you warm your cassettes, prior to adding the plasma and red cells, it will still not be at 37^oC, as you have to take the cassette out of the incubator before you add the plasma and red cells.

 

Thirdly, the gel/glass beads in which the AHG is suspended is slightly acidic, and anti-M just LOVES acidic conditions, and so will react more strongly with M+ red cells in such conditions.

[MAGNUM]

When I was using gel and suspected that I might have a M playing around in my plasma, I would actually prewarm the gelcards and actually inoculate them while in the incubator that way, the card was hopefully at a constant 37.

[Malcolm Needs ☆]

I am prepared to bet it wasn't MAGNUM!

[pstruik]

We used to do as Magnum and although I never claimed everything was at 37C - as Malcolm in his tedious way is quite correct to point out it almost certainly wasn't - it was all what we scientists describe as 'warm' and allowed suitably crossmatched blood to be provided for such patients with a minimum of fuss, tantrums, tears, doubt, worry or referral to a 'proper' Transfusion laboratory with experts and waterbaths and tubes like what Malcolm has

[Malcolm Needs ☆]

Tedious indeed Peter - you mean PEDANTIC Sir!!!!!!!!!!!!

 

Anyway, we (NHSBT) now recommend giving M- blood - even though it is NOT required in more than 99% of cases!

[Auntie-D]

Secondly, even if you warm your cassettes, prior to adding the plasma and red cells, it will still not be at 37^oC, as you have to take the cassette out of the incubator before you add the plasma and red cells.

 

 

When I was using gel and suspected that I might have a M playing around in my plasma, I would actually prewarm the gelcards and actually inoculate them while in the incubator that way, the card was hopefully at a constant 37.

 

We do this too - and incubate for slightly longer to allow dissociation to have a chance of happening.

[Malcolm Needs ☆]

Be careful though Auntie-D, because if your incubation time is longer than that prescribed by the manufacturer, and anything goes wrong (God forbid), then you become the manufacturer, and you will be sued, rather than the company who produces the cards.

[Auntie-D]

Be careful though Auntie-D, because if your incubation time is longer than that prescribed by the manufacturer, and anything goes wrong (God forbid), then you become the manufacturer, and you will be sued, rather than the company who produces the cards.

 

Cards say a maximum incubation time of 30 minutes which we do not exceed