Was wondering if I could get some comments on the current use or non-use of the prewarm technique. Within the past couple of years the procedure has been the recipient of multiple slings and arrows by a few noted authors in the field.

Personally, coming from a reference lab which deals almost exclusively with prenatals, I still find it hard to believe that an anti-M which is prewarmable could possibly have any effect during pregnancy. Obviously these screens should be followed up periodically to exclude the development of a warm-reactive IgG anti-M but at what point do we simply avoid titers in these cases? The problem with reporting titers with these specimens is that unless something like DTT or 2ME are employed one is giving the physician a titer which is falsely elevated due to IgM activity. Admittedly some of this reactivity may be due to IgG antibody which is non-reactive at 37C, but how relevant would that tend to be?

In any case, any comments regarding your protocol for both prenatals and transfusion candidates would be of interest. Thanks!

In any

Hi. The question of the age. The institution I currently work at does not believe in the use of prewarm technique. We use gel as our screening method and if pos we work up the antibody in peg. If it then appears to be a CAA or something of that nature, then we do weird things like omit I.S., and repeat, if still pos, then we try 30 min no enhancement screen without IS. If not negative we use REST for untransfused people and redo screen, or differential absorption for patients who have been transfused.

If we name it like Anti-M, Anti-P etc., and it is a prenatal sample, then we first decide if the antibody is IgM or IgG or both and use DTT treated serum. The antibody must react with a heterozygote cell in order for us to consider a titer and it must be clinically significant (IgG).

I hope this helps you.

Though used rarely, we still rely on PW technique when it is indicated. Using EDTA specimens has cut down the number of cold agglutinins we encounter, however, in Northern NH, where we are located, most of the small hospitals still use serum. As their local reference lab, it is important for us to realize this . . . and we have found more often than not a negative absc using plasma but significant reactivity with serum. The BIGGEST problem I have encountered is that the small places have a PW technique procedure but their staff modifies" it to the extent that it is useless. And you know, those demigods of blood bank poo-poo it, but I feel it is still a valuable assay when used correctly.

I agree that there is widespread misuse of the prewarm technique. We have missed clinically significant antibodies with this method.

I think the real answer is to omit the immediate spin reading everywhere except the backtype. No IS reading for antibody screens. Electronic crossmatch needs to replace the IS crossmatch. Full crossmatches should not have an IS reading. That way we will be less likely to see cold antibodies. If they are truly clinically significant they will show up at 37 and/or AHG. ABO antibodies have absolutely no problem showing their faces at 37 and AHG, so that should not be a worry.

When I first came to the lab where I currently work, the pre-warmed technique was being used every time someone saw weak reactions.

That's the kind of use that got the technique "poo-pooed".

I went to a great lecture not long ago by George Garrity who expressed his agreement that there really was no place for the pre-warmed technique in routine blood banking. He did say that in the reference lab setting, expecially when dealing with Auto's, it might be useful.

We have switched to plasma, don't do immediate spin, or 37 readings on any of our screens and we have done away with pre-warmed technique.

After reading that 37% of significant antibodies were missed when the pre-warmed technique was used, that was enough for me to stop it's use in our lab. If our I.S. crossmatch shows agglutination, we just do a "mini-cold panel" including cord cells to show Anti-I and then XM through AHG.

If you are using gel there is very little need to pre-warm in the hospital blood bank. I recommend to our staff that pre-warm be done only in instances where we have demonstrated the presence of a cold auto-antibody AND no alloantibody is detectable using a PEG panel in the tube procedure. We also do a gel panel using the Ortho A panel to initially identify those antibodies that are not of IgM/complement specificity.

Gel methodology has been the prevalent technique for most of the facilities where I've worked these past few years. On occasion, have encountered cold antibodies showing up even in gel...these having a diffuse pattern and variable reactions. Employing the prewarmed tube method with LISS has taken care of most cold antibodies in my experience and I've not yet see any conflict between my results with either previous workups or with specimens collected later and worked up by co-workers or at reference labs.

But since I'm no expert! for those interested, perhaps another voice would be helpful:

"Applied Blood Group Serology" (Issitt, Anstee) 1998, 4th ed. pp. 881-882. Issitt states that if the pre-warmed technique is missing significant antibodies, then perhaps that's due to a lack of potentiator in the incubation phase vs. something inherent to the technique itself. In earlier AABB technical manuals, the prewarmed technique omitted a potentiator, whereas in the most recent (15th ed.) pp. 691-692, a note was inserted suggesting the use of a potentiator (LISS, albumin or PEG) with the caveat that cold reacting antibodies might be potentiated along with any significant antibodies.

Like any BB technique, pre-warming has its use and misuse, and requires interpretation in light of the other facts surrounding the sample. Pre-warming (like its counterpart, the dreaded RT or cold panel) can play a wonderful role in separating antibodies if one is more cold-reacting and one is more warm-reacting, like an anti-M combined with an anti-Fya.

However, I've worked for places that pre-warm just about every positive reaction, calling the pre-warm negatives a "cold antibody." Dangerous ...

My last SOP called for cautious use of pre-warm technique in certain situations; my current one leaves it up to the judgment of the technologist.

To return to the initial question of whether to titer a prenatal anti-M, we will use the pre-warm to decide whether to titer or not. We do not titer if the antibody pre-warms away or if the strength of agglutination is less than 2+. We do not use the pre-warm to identify the antibody, only to determine whether to titer or not.

I'm curious, does anyone know what kind of clinical decisions a physician will make base on the titer of an anti-M or most any other antibody excluding anit-D? Considering, to my knowledge, anti-D is the only antibody to have been studied and clinical outcomes reflected by titer values established.