unexplainable cell reaction

[gilmanch]

What is your procedure for a random cell that is reacting and not accoutanted for? Our testing capablity is limited with simple ABID. I am still trying to figure out a happy balance for us for sending things and not sending things to a reference lab. I know at where I used to work we didnt sent a lot of those one random cells for further investigation. Would just assume low incidence or HLA(if postitive on the extended) and be done giving IgG XM. But I did not know what I know now and knowing what I know now...makes things harder sometimes!! haha

Is it more important with the pregnancy patients. How about with patients who have been transfused ever?

 

Talking with red cross they would confirm the HLA by treating with something that destoys the antigen to show no more reactivity

 

So wondering if write the procedure say:

1. any unexplanable cell and patient pregnant and or transfused hx must go to reference lab even if all commonly encountered are ruled out

2. any unexplanable cell and pt not pregnant or transfused and all commonly encoutered are ruled out give IgG xm

Thoughts, ideas appreciated, thank you!!

[Malcolm Needs ☆]

My own thoughts, for what they are worth, is that, unless it is a pregnancy, I would just give IgG XM blood.

It is terribly difficult and time consuming for a Reference Laboratory to identify the exact specificity of an antibody directed against a low prevalence antigen, for very little return (except, of course, treating the patient's red cells with chloroquine to destroy adsorbed HLA antigens), when it is easy to find crossmatch compatible blood.

In the case of pregnancy, it would depend upon the strength and titre of the antibody against the one cell as to how we would test the sample.  It would be useful to 1) get any history of previous pregnancies and if there is any history of HDN, 2) to find out the ethnic origin of the lady, and 3) test the male partner's red cells against the maternal plasma, if they are ABO compatible.  If they are not, it makes life harder, but does not make life impossible, in that you can get rid of the ABO antibodies by either neutralisation against ABO substance, or by adsorbing out the ABO antigen with appropriate red cells.  If you use adsorption, it is probably worthwhile splitting the maternal plasma sample into at least two aliquots and performing the adsorption with two different sources of red cells of the appropriate ABO group, because if you just do it with one, you may be unlucky and this one example may also express the cognate low prevalence antigen and adsorb out the problem antibody, as well as the ABO antibody, but you would have to be very unlucky indeed to choose two cell samples that both express the cognate low prevalence antigen (although, never say never!!!!!!!!!).

[gilmanch]

Malcolm:

I can perform titers here. So would this be a good procedure?

 

1. if all common ruled out and not pregnant give XM compat

2. if pregnant do titer. if titer = (insert number here)  monitor titer with draw in 2-weeks

                                if titer = (insert number here) send to ref lab

 

OR

 

1. if all common ruled out and not pregnant give XM compat

2. if prenant send to ref lab

 

OR

1.  if all common ruled out and not pregnant give XM compat

2. if prenant have the dad drawn

I feel that, even thou sounds very simple and helpful, our staff/resources should not be testing the dad with the mom due to the fact that ABO could play a role and having to adsorb/neutralize. I have techs that have never peformed and question would be the understanding of what is going on when doing that. I could write procedure to do ABO on dad first. if compat blood types do xm with mom. if not compat send to ARC. I am then also at what is that telling me when doing the XM with mom and dad. if it is positive then it is more likely an antibody to a low prev antigen and if negative then more likely the HLA?? Where would I go from there? Still send to the ARC?

Thoughts again, b/c it is always appreciated!

[jayinsat]

What methodology are you using for antibody screening and identification?  Is there a significant rate of unexpected positive reactions with this methodology?  That helps determine how far down that rabbit hole I will travel. 

[gilmanch]

GEL METHOD

[Malcolm Needs ☆]

The titre is, in a way, a dicotomy!

If the patient is not pregnant, but is to be transfused, the higher the titre, and the more avid the reaction, the better, as, if the titre is high and the reaction is avid, it can give you much greater confidence that the crossmatched units will be efficacious if the crossmatch is compatible.

If the patient is either pregnant, or is pregnant and requires a transfusion, the lower the titre, and the less avid the reaction, the better, as it is unlikely that the antibody will cause clinically significant haemolytic disease of the foetus and newborn if the titre remains below 32 (although, of course, this is not definitive, as antibodies directed against antigens within the Kell Blood Group System have a poor correlation between titre and the severity of HDFN).

When, and indeed, if, another draw is required depends upon a number of factors.  The first is any past history of HDFN, The second is, again, the titre.  The third is the stage of the pregnancy.  The fourth is the specificity of the antibody.  The fifth is whether or not the cognate antigen is well-delevoped on foetal red cells.  The sixth is whether or not the male partner is expressing the cognate antigen on his red cells.  So, let's go through these one-by-one.

If there is a past history of HDFN, then the titre needs to be monitored on a very regular basis (even if the present titre is low), but really only after 28 weeks of gestation.  If there is no past history of HDFN, this is good (even if this is the first pregnancy - as HDFN, other than ABO HDFN, rarely occurs in a first pregnancy), as it suggests that the antibody is not particularly clinically significant.

If the titre is high (32 or greater), then there should be a redraw at 28 weeks of gestation, or as directed by the Blood bank Director if the pregnancy is greater than 28 weeks of gestation.  If the titre is low (<32), and/or the pregnancy is >32 weeks of gestation, then there may not need to be a redraw (depending on the other factors).

If the specificity of the antibody can be established (and this may have to be done at a Reference Laboratory, who may have access to many different red cells expressing low prevalence antigens, or may even have access to recombinant blood group proteins that may aid in identification.  If the specificity can be established, then the literature (such as The Blood Group Antigen FactsBook) should tell you whether or not the antibody has been implicated in HDFN.  Such literature should also tell you if the cognate antigen is either well expressed or poorly expressed on foetal red cells.  If it is poorly expressed, then clinically significant HDFN is very unlikely.

Telling whether or not the male partner expresses the cognate antigen on his red cells (and so can pass on the cognate gene to the foetus) depends on whether or not the specificity can be established, or, failing this, reacting the male partner's red cells against the (possibly, adsorbed) maternal plasma.

This all suggests to me that a sample should be sent to the Reference Laboratory.

Failing all of this, a cellular assay, such as MMA, could be undertaken, to see if the antibody of unknown specificity is likely to be clinically significant, however, although the results of this seem to correlate quite well with the survival of red cells following a transfusion, they do not necessarily correlate well with severity of HDFN (for example, anti-In^b is predicted to cause HDFN by MMA, but it does not, as it is adsorbed onto the apical surface of the placenta).

 

I hope my ramblings are of some help.