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Down the Memory Lane - The Prewarming Procedure

A Blog from Eric Ching:

Dear Colleagues,
Hope everyone has had a nice summer break. My first two months of retirement were wonderful - tidied up my office, threw away tons of papers, painted my decks, traveled for fun instead and ate a lot! I guess it’s now time for me to polish my brain a little bit.J
I was asked by Dr. Gwen Clarke to comment on the Prewarming Procedure recently; after pondering awhile, I put this under the Down the memory lane category even though I know it is not an uncommon procedure, still favoured by many colleagues. Below is my view on the subject and I hope you will understand why I put this subject under the above category.
Until the question of “clinical significance” of blood group antibodies was raised in the mid to late 70’s, blood group serologists were accustomed to identifying all antibodies, regardless of temperature preference. At the Calgary Red Cross, we even tried to split hairs to see if the antibody was auto-HI or -IH!
For the first few years at the bench, whenever we encountered inconclusive panels, we were taught to use the prewarm technique to get rid of the “non specific” reactions. The practice of “prewarming cells and serum at 370C before mixing, incubate, skip the spin and read after incubation and wash with warm saline” was deemed safe and was routinely performed.
Looking back, when we used serum and “broad spectrum” rabbit anti-human globulin, the incidence of coming across a cold reactive autoantibody among patient samples was much higher than what we see nowadays.
Since the common adoption of use of anti-IgG in the late 70’s to early 80’s, the frequency of using prewarm had reduced significantly. Even so, prewarm has perpetuated because of the common belief that it is a good means to circumvent non-specific reactions. Such practice has indoctrinated many blood bankers including myself.
As I gained more experience, I realized that I didn’t have any data to support the notion that those so-called non-specific reactions were caused by cold reactive autoantibodies; I just assumed it was most likely the caseL!
In the early 90’s, like most major blood banks in western Canada, we started using PEG as an additive for IAT; we noticed that the prewarm was used more often than the days of using LISS-IAT. Although PEG-IAT was popular in the west, colleagues in central Canada had not embraced PEG because of issues with specificity. That was the time that I asked my staff to look for laboratory evidence of the presence of cold reactive antibodies interfering in the antibody screen, crossmatch and antibody identification (we were still doing full crossmatch in the early 90’s).
At the 1992 CSMLS meeting, Robert Fallis presented his findings on “PEG macro” which is the use of PEG-IAT with macroscopic reading only.  In his presentation, Bob’s data showed that PEG macro has better sensitivity and specificity than PEG micro, LISS macro and LISS micro. 
Although we experienced a decreased use of prewarm after the adoption of PEG macro as a routine, I still suggested to my staff to set up the following test to indicate cold and sometime warm reactive autoantibody:
  • Cold agglutinin Screen
  • DAT
  • Enzyme treated  cells
Cold Agglutinin Screen (see previous blog)
Reactivity 2+ or less does not interfere in IAT using anti-IgG (my personal experience, no data to support my claim)
If it was 3+ or 4+, we would prewarm ( I didn’t know it would compromise sensitivity, I hope someone can offer a good explanation as to how and why? L). I now recommend the use of rabbit red cell stroma to adsorb the cold reactive autoantibody.
Presence of complement on patient red cells lends more credence to the presence of a cold reactive autoantibody.
Enzyme treated cells
Papainized or commercially available ficinized R1R1 and R2R2 cells can be used for the antibody screen to see if reactivity is enhanced in the case of cold or warm reactive autoantibody or a weak but clinically significant Rh or Kidd system antibody. Abolished reactivity may indicate the non-specific reactions could be due to Duffy, MNS, Roger/Chido just to name a few.
Since the advent of routine use of solid phase red cell adherence assay as well as computer assisted crossmatch in the mid 90’s, the prewarm techniques became rarely used. Perhaps other solid phase users can share their experience with us. Around that time, there was debate amongst blood bankers whether prewarm was a useful procedure to provide timely transfusion as there were case reports of missing clinically significant antibodies with prewarm. With our routine use of solid phase, prewarm was not an issue in our blood bank.
Those who are interested in this topic can read the pros and cons of the prewarm technique in Transfusion 1995;35: 268-275.
Leger and Garratty’s paper on the weakening (40-47%) and a 14% complete loss of antibody activity published in Transfusion 2003; 43:1611-14 echoed Judd’s earlier abstract, which indicated that sensitivity could be compromised by as much as 23% (Transfusion 1995;35: 68S).
I wonder who could give us an explanation of this phenomenon as it defies my understanding (or lack of) antigen antibody interactions. It was shown in Leger and Garratty’s study that neither the enhancing media nor low affinity of the antibodies was the reason.
Although in certain clinical situations the use of prewarm is justified, this entry reminds us of the potential risk when we use prewarm.
Again, communicating with clinical staff is important to see if the patient can the wait for blood bank to identify the presence of a cold agglutinin and have other means to bypass its interference.
It would be nice to see a project done on the incidence of a collection of known cold reactive autoantibodies  causing interference to various routine methods (or better yet, a prospective study).


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