Anti-M again

[jojo808]

Regarding an Anti-M that is showing dosage: 

I understand from reading older posts that an Anti-M is considered clinically significant if reactive at 37C and most would consider transfusing with M negative units in those situations. Would it be correct to say that if your Screening cells did not possess a MM cell for this dosing M to react with, you wouldn't even know you had an antibody even if the anti-M was reactive at 37C? Some posts stated that they do not type units for M but transfuse random units compatible at IAT. In these cases where you are choosing random units, the dosing anti-M would be non-reactive with the MN units and reactive with the MM units. So, you would end up giving "compatible" M positive units (hetero expression) could that cause any problems later?  I also wondered that if your Anti-M is prewarm negative, and you give random IAT compatible units and let's say the units are MN and are "clean" in the crossmatch (prewarm or not) and we are transfusing a unit straight from the (cold) refrigerator ... would that cause binding in vivo? Does it matter if the M is prewarm negative or positive if your policy is to transfuse M negative units anyway?  Sorry for all the questions, I thought I had it down but then someone challenges the process, and it gets you thinking again. Thank you in advance! 

[Malcolm Needs ★]

In the UK this problem should not occur, as our BSH (BCSH) Guidelines mandate that our screening cells have homozygous expression of certain antigens, one of which is M.

[jayinsat]

Theoretically, you could have in vivo binding. Practically, I've never seen it happen. We do not type for M antigen and give xm compatible here. 

 

[Ensis01]

For many hospitals; once an anti-M is identified, at any phase, M neg units are required. This is usually due to reluctance, or inability to over-ride the BB LIS especially if the BB is primarily staffed by generalists. 

[Malcolm Needs ★]

13 hours ago, Ensis01 said:

For many hospitals; once an anti-M is identified, at any phase, M neg units are required. This is usually due to reluctance, or inability to over-ride the BB LIS especially if the BB is primarily staffed by generalists. 

What a waste of expensive phenotyped blood.

[Neil Blumberg]

As a general rule, an anti-M that doesn't react with heterozygous cells probably isn't very biologically potent or clinically relevant, so that's my take on that issue.  We honor anti-M antibodies that react at 37 or antiglobulin phase, but many of these probably would not cause significant hemolysis in all likelihood. 

[Malcolm Needs ★]

42 minutes ago, Neil Blumberg said:

We honor anti-M antibodies that react at 37 or antiglobulin phase, but many of these probably would not cause significant hemolysis in all likelihood. 

True, but who is going to perform tests, such as ADCC, that cost a certain amount of money, as well as time, when M Negative units are generally easily available?

[Neil Blumberg]

Agreed.  We don't use the ADCC, we just give M negative.  Even a little, sub-clinical hemolysis probably isn't good for patients :).