Definition of weak-backtype ...when to full crossmatch?

[lab217]

Does a weak backtype (less than 2 + reaction)

necessitate a full coombs crossmatch? Talking to other blood banks in my area, it seems our blood bank is the only one doing this. The thought is that less than a 2 plus reaction may indicate an impairment of the patient to produce antibodies. Any suggestions or ideas would be greatly appreciated.

[Brenda K Hutson]

I have never heard of that protocol (performing a coombs crossmatch due to a weak backtype). There can be many perfectly "normal" reasons for a weak backtype (i.e. age; bone marrow transplants; and yes, immunodeficiency). However, you are still performing some type of coombs Antibody Screen, so I personally would not initiate a policy like this.

But if there is anyone out there doing this, I would be interested in your rationale....

Brenda Hutson, CLS(ASCP)SBB

Does a weak backtype (less than 2 + reaction)

necessitate a full coombs crossmatch? Talking to other blood banks in my area, it seems our blood bank is the only one doing this. The thought is that less than a 2 plus reaction may indicate an impairment of the patient to produce antibodies. Any suggestions or ideas would be greatly appreciated.

[Yanxia]

We will not do full crossmatch because the weak backtype.

If it is weaker than 2+, we will do some test to see if there is some subgroup of AB.

[rravkin@aol.com]

Lab217,

In speculation of the practice you present I think that the rational for it may be to conservatively assure that the donor unit is compatible in light of the potential immune compromise demonstrated in the backtype whereby a potental weakened allo antibody may not be detected through the antibody screen; the logic of which comes from the idea that if your ABO antibodies are attenuated in any way then any of the other allo antibodies would follow suite; and a weakened allo atibody although not detected through your reagent screening cells may be otherwise detected through the extended crossmatch with your donor cells which are not prepared and preserved as your reagent screening cells are; and not to mention also that the difference in cell surface antigen distribution is almost definitively different between the screening and donor cells which may also have an effect on reactivity. In short, I think that this practice is basically a highly conservative effort to assure a compatible crossmatch in light of the implications of a weakened backtype. I have to say that I have never worked anywhere that engaged this practice but I think that we can at least speculate why.

I hope this helps a little.

[David Saikin]

I do the full/ahg xm only when the backtype is undetectable at immediate spin. I will endeavor to produce a backtype (cold/enzyme/etc) BUT the purpose of the IS xm is to detect ABO incompatibility. If the routine backtype does not do this I expect the routien ISxm will not either. I am unaware of other institutions that follow that protocol.

Edited August 22, 2011 by David Saikin
spelling

[csjuarez]

I can understand such a protocol if the backtype is undetectable and a coombs crossmatch is not otherwise required. However, if you are using a computer system for crossmatching, it should already have the protocols integrated to assure ABO compatability and such a serological protocol should only be needed during downtime.

[David Saikin]

True - but only if validated for e-xm.

I can understand such a protocol if the backtype is undetectable and a coombs crossmatch is not otherwise required. However, if you are using a computer system for crossmatching, it should already have the protocols integrated to assure ABO compatability and such a serological protocol should only be needed during downtime.

[Mabel Adams]

And if gel is your AHG xm, you are not supposed to count on it to detect ABO incompatibility, which could be a point of concern in someone with a weak reverse. Also, since screen cells are tested to make sure they have a consistently strong expression of at least the usual antigens (homozygous etc.), I would trust them to pick up weak antibodies more readily than a cell from a heterozygous donor.

[AVANHORN]

We have a policy here that we do a full AHG crossmatch in tube using enhancement if the backtype is <1+ with IS crossmatch.  This is to detect ABO incompatibility as that is the purpose of doing an IS xmatch.

 

[Malcolm Needs ☆]

That's all very well AVANHORN, but the optimum temperature for ABO antibodies is between 0oC and 4oC, so, if you are not detecting the the reverse anti-A and/or anti-B at room temperature, because it is weak, there is no guarantee that you will detect it after incubation at 37oC, even with enhancing agents.

 

It may be just a sop, rather than a valid test.

 

I would be inclined to issue group O blood under such circumstances.  That way you are safe (apart from an Oh patient, of course, but how many of those are you going to see)!

[Auntie-D]

I don't understand the rational of all this ABO vs allo and if the ABO antibody is weakened then the allo will be too - one is IgG and one IgM (usually) so it's like comparing apples and oranges...

I've seen numerous haematology patients with no back group with strongly expressed allo antibodies.

Here's one for you - we don't even do reverse grouping after the first presentation - and we electronically issue