Anti-M

[Eloise]

Hi to all!

I'm wondering about Anti-M. We have a couple of patients who have had reactions in gel that were later identified as Anti-M. (We send all of our antibody identifications to a reference lab for work-up.)

The latest patient had positive reactions by tube method at RT, 37 degrees, and AHG (Ig-G). The reference lab performed a prewarm technique and has stated that this antibody is not a clinically significant antibody because it prewarmed away.

From what I've found in the AABB technical manual, if the antibody is demonstrated through AHG as this one is, then it is clinically significant and you can't eliminate it because the prewarm technique has been known to eliminate clinically significant antibodies.

My training has been to always transfuse antigen negative blood when an antibody is identified.

I was wondering if anyone has any thought about this and how they hand patients with anti-M.

Thanks in advance.

Eloise

[Eagle Eye]

We give Gel IgG crossmatch compatible units we do not screen for antigen M.

[cinbb]

I concur with aakupaku. We also perform IgG gel IAT crossmatch for patients with Anti-M. Then issue only IAT crossmatch compatible units. We do not antigen screen the recipient or the donor unit for M antigen. Again, most experts conclude Anti-M is not clinically signifigant. Performing the IAT crossmatch would eliminate any donor unitreactive at 37 degrees/IAT.

Good reference: "Blood Group Antigens & Antibodies" by Reid and Lomas-Francis

[tbostock]

If it's in gel, we honor it, and screen units and do full crossmatches in gel.

[bxcall1]

From Issit, Applied Blood Group Serology - "There is no need to type donor units for M and N and select those units that lack the appropriate antigen. Instead, the patient's serum can be used in IAT, prewarmed to 37 degrees if necessary, and those units found to be compatible can be transfused with impunity."

From this we developed our policy re: anti M. "Patients demonstrating anti-M may be transfused using crossmatch compatible units. Screening for M negative cells is not required."

[Eloise]

I forgot to say that likke many anti-M antibodies, this patient's antibody is showing dosage, i.e. only reacting with homologous M panel or screen cells.

My thanks to all who have responded.

Eloise

[yolis76]

The reactivity seen at AHG could be carryover from the strong reactions at IS... I would have to see the reaction strengths to see if this is possible. But at the same time, we use Solid phase, and because this methodology claims to only pick up IgG antibodies, we identify a few Anti-Ms a year using SP. If we test these same patients using tube you can clearly see its only a cold reacting anitbody, so why are we seeing reactivity in SP? The manufacturer has suggested that the indicator cells express M antigen, and therefore the M antigen on the indicator cells is causing the reactivity. I have done some additional testing to see if this is the case, but I have not had conclusive results. We don't have any DTT to test the patient serum and see if we can separate IgG from IgM. Our medical director is wary about not giving M neg units, so if the Anti-M reacts in SP we automatically give M neg units with AHG XM, even if the tube testing clearly shows cold antibody.

[eeagan]

We always do a AHG crossmatch on patients with anti-M. We also always do a prewarm screen on M+ cells that reacted at AHG. We use PEG for our manual antibody screens. If the prewarm screen is negative, we rely on the crossmatches for compatible units. If the prewarm screen is positive, we crossmatch (PEG to AHG) M negative units. This policy was started recently by our medical director who feels that the results of the prewarm screen will show if the anti-M is IgG or IgM. So far, I cannot recall one patient whose anti-M was prewarm positive.

[Malcolm Needs ☆]

There are two things to remember about this.

The first is that "cold" reacting antibodies can sensitize red cells extremely quickly as the tests are set up. The gel tests are usually set up at room temperature and then moved to a 37oC environment for incubation, and then the centrifugation at the end of incubation is performed, once again, at room temperature. Therefore, "cold" reacting anti-M's (and "cold" reacting antibodies of other specificities) have plenty of opportunity to sensitize (and, therefore, agglutinate) red cells during the gel IAT, but, this is a kind of "false positive", as such antibodies are not truly "warm" reacting.

The second thing is that, to a certain extent, the immunoglobulin class of the antibody is irrelevant, as some IgG antibodies react optimally in the cold (for example, the anti-P in PCH - the antibody itself is not what causes the problem here - it is the overlap of the temperature at which the antibody reacts and the temperature at which complement is activated - hence the bi-phasic temperature test).

My own, very strongly held view is that, unless an anti-M reacts by the tube IAT technique, performed strictly at 37oC, we pre-warmed plasma and red cell suspension prior to mixing, and washing with pre-warmed saline prior to the addition of the AHG, it is not clinically significant, and cross-match compatible blood is more than suitable.

[David Saikin]

I agree with Malcolm

[Bill Sinn]

We do AHG crossmatches in gel for patients with Anti M. We do not screen units for M antigen. It helps to find compatible units if you prewarm the gel card, the donor RBC suspensions in MTS Diluent, and the patient's plasma before combining in the gel card. Some of these compatible units may have heterozygous expression of the M antigen, but we don't care.

Bill Sinn

[Eloise]

Thanks to everyone for writing!

Eloise

[ckcheng]

I agree with Malcolm Needs. I just came across an example of anti-M which reacted with homozygous M-pos cells and gave a 2+ reaction with gel, but negative with heterozygous cells. Problem also seen in reverse grouping. I prewarmed plasma and screen cells separately at 37C for 5 minutes before mixing, then washed with pre-warmed saline 3X after 45 mins incubation. The screening was negative. I issued blood with EXM.

One question I wanna raise is that when the patient is going to have an open heart surgery, and the cold reactive anti-M does potent enough to interfere at room temp, should we add a comment to alert the transfusionist to pre-warm the donor blood before transfusion cuz the M frequency in Whites is around 80%?!

CK Cheng, MSc, SBB(ASCP), CQA(ASQ)

Hong Kong

May 6, 2009

[LaraT23]

IN open hearts, the patients core temp will drop. There is not way to really know that an Anti-M will continue to be " not clinically significant:" during that circumstance.

In my department, we do screen for M simply because we may have only one person in the department at a time and no one but myself will prewarm and wash with warmed saline and then do a full XM without screening. They are all really freaked about that. So, I just tell them to screen for M and do a full XM on neg units. Our medical director is goosy about that as well so we just make him happy.

[PammyDQ]

If it's in gel, we honor it, and screen units and do full crossmatches in gel.

DITTO...

But aren't M's a pain in the b*u*t*t*...I'm working on finding M negative units for one now

Edited May 6, 2009 by PammyDQ
i can't believe the word b u t t was censored LOL

[Joanne P. Scannell]

Given these facts::

1. Gel is known to enhance Anti-M because it is more acidic than tube testing; that's why we are seeing more of them now.

2. Anti-M is not considered clinically signficant although there is debate how signfiicant the antibody is if it has a high thermal amplitude, eg. reacts at 37oC.

Having these in mind, we do the following (as I see some of you in here also do):

If we identify Anti-M using gel, we repeat using Prewarm Technique using TUBE testing, eg. PEG, with a 'homozygous' M-pos cell. If this is negative, it is a cold agglutinin and treated as such (let's not go there right now). If it is positive, it is a warm antibody and treated as such ... that is, full crossmatch using pre-warm with TUBE testing (gel will enhance!) and issue the crossmatch compatible units. No reagent Anti-M testing is done ... as expressed in here earlier, it is not necessary.

I agree with the note about 'Open Hearts' ... we do the same ... just as for any cold agglutinin. But, like I said, that's another thread to unwind!