Anti M with solid phase on TANGO

[catchmenow51]

I know as I write this post, I will be different than most. With that being said, the IRL I work at performs type and screens in tube and panels in gel. That way when we detect an anti-M in gel, we know where it's reacting. We do not consider anti-M clinically significant unless it is reacting at 37 or greater. The only time we don't push to ignore the M is when it is a heart patient.

[Malcolm Needs ☆]

We do our screens and identification in gel. Would it be a good idea to perform them in tube before reporting out an anti-M on a prenatal patient. We sent out a titer once a month on a pregnant woman-the titer was always too low to quantify. I don't want to miss anything, but I hate to think of the expense as well. We are now sending out a specimen to anti-U, anti-N and anti-Leb titer.

Thanks, Mari

 

Hi Mari,

 

My answer would be "yes, perform your anti-M in tube, using pre-warmed red cells and pre-warmed plasma, and washing with pre-warmed saline."  Anti-M in pregnancy, or in any other situation, come to that (including cardiac surgery) is only clinically significant if it reacts STRICTLY at 37^oC.

 

You have to remember that anti-M "loves" a low pH, and gel columns usually have a low pH (which is why the technique detects so many).  In addition, the anti-M can sensitise the M+ red cells extremely quickly (as you are setting up your tests at room temperature - before you incubate at 37^oC), and the short incubation period is insufficient for all of the anti-M to elute back off.  Then, you centrifuge your cards at room temperature again.  You will, therefore, often get a "false positive" (in terms of clinical significance) with the gel technique.

 

Anyway, turning to the other part of your post, why on Earth do you titrate your anti-N and anti-Le^b sera (or send them away for titration, should I say)?  A clinically significant anti-N is an exceedingly rare animal (I've seen about three in 42 years of working - and even then, it was more a transfusion problem than an HDFN problem), and anti-Le^b is usually IgM (so it won't go through the placenta) and, even if it was an IgG case, Lewis antigens are extremely poorly expressed on foetal red cells.  As far as I know, there has only been one case report in the literature involving anti-Le^b causing very mild HDFN (and even that was a bit dubious!).

 

I agree entirely with you sending off cases of anti-U - not least, because I doubt whether you would have sufficient rare cells to exclude other alloantibodies - in particular, those within the Duffy Blood Group System.

 

Sorry for the rant - which is now well and truly over!!!!!!!!!!!!

[mollyredone]

Malcolm,

We just send out the specimen and the reference lab titrates the necessary antibodies. They don't titer anti-N or anti-Leb, and the anti-U is too weak to titer right now. But how unlucky is this patient!?!

[Malcolm Needs ☆]

Oh sorry Mari, I got COMPLETELY the wrong end of the stick.  I read it as you send samples from separate patients who have anti-U, patients who have anti-N and patients who have anti-Le^b,  I certainly should have known better of you.

 

Actually, the patient isn't that "unlucky", in that, if the patient is M+, N-, S-, s- U- (as I would expect in such a case), and they would also, therefore, be 'N'-, then I would expect them to make an anti-N, as well as an anti-U.

 

As for the anti-Le^b, that is not unusual in pregnancy, as the pregnant lady will "lose" her Lewis antigens during pregnancy, and it would not be unusual to see Lew is antibodies in the plasma.

 

The trick, under such circumstances, is ruling out other clinically significant antibodies!

 

Again, I apologise for my misreading of your post (and my stupidity in so doing).

[Transfusion98]

We evaluate every anti-M, each time, for 37 degree reactivity. Not taking any unnecessary risks. Although I still have a few techs who will screen units regardless of clinical significance on the basis of "I see it, so I can't ignore it."

[galvania]

Back to anti-M in gel.  If anyone wants to be sure that they have an anti-M, the best way to do it is to incubate your Coombs cards at room temperature for 10-15mins. a wishy-washy result will turn into a nice 3-4+.

More difficult to carry out gel STRICTLY at 37°C.  But this is what I would do.  Incubate cards, cells, plasma and pipette tips at 37°C for at least 15mins before pipetting.  Run your centrifuge empty (or full with other things) at the same time.  Pipette as far as possible IN the incubator (not easy, but do-able).  Keep running the centrifuge while the cards are incubating.  After incubation JUST put those cards in the centrifuge - or if you have other cards, put those in the centrifuge first, to minimise the time spent at RT, and start the centrifuge immediately.  This will get rid of all but the most tenacious cold anti-M.  Good luck!

[David Saikin]

Anna

 

I can look for M's with just the buffered card if I'm going to do a RT incubation. 

I don't think you can do a STRICTLY prewarmed technique in cards, though your procedure is plausible - I just do the PW in tubes.  I use an i.s. in tube also  just to verify that the ab is reacting there.  I just had to do this with an anti-N, worked just as well.

 

Malcolm, I wasn't going to stock anti-N any longer WHEN I had one that I could not Prewarm away . . . wouldn't you know.