Pre transfusion testing guidelines 2012

[Tabbie]

Hi All

Just a few questions on ruling out. Section 6.2.4 describes at least two examples expressing the antigen 

I am assuming this applies to IAT and Enzyme testing reactions separately (assuming antibody reacts by enzyme) and also that this can be homozygous or heterozygous expression of the antigen ? It does state in 6.2.6 that a single example can be excluded if homozygous for anti Jka/Jkb, S/s and Fya/Fyb.

Thanks

 

 

Edited August 29, 2016 by Tabbie

[Tabbie]

 

Also has anyone excluded a heterozygous anti-C negative in IAT and 1+ in enzyme (because in theory Rh should be enhanced). The panel also has an anti-D and Jkb

Thanks

[Malcolm Needs ☆]

14 hours ago, Tabbie said:

Just a few questions on ruling out. Section 6.2.4 describes at least two examples expressing the antigen 

I am assuming this applies to IAT and Enzyme testing reactions separately (assuming antibody reacts by enzyme) and also that this can be homozygous or heterozygous expression of the antigen ? It does state in 6.2.6 that a single example can be excluded if homozygous for anti Jka/Jkb, S/s and Fya/Fyb.

Hi Tabbie,

You are correct in saying that the two techniques should be taken separately, but the reason that paragraph 6.2.6 mentions the antigens Jk^a/Jk^b, S/s and Fy^a/Fy^b in particular is that these are the antibody/antigen combinations that show "dosage".  However, I'm afraid that I disagree with the Guideline when it states that a single example of a red cell showing homozygous expression of the antigen can be used to exclude a specificity, unless the donor has been genotyped to ensure homozygous expression of the relevant gene, and I know that NHSBT (at least) does not do this (although it does test expression by flow cytometry (I've never seen this proved as a way of demonstrating a "genotype", I have to say).  Unless a genotype is undertaken, then a donor who has the phenotype, for example, Fy(a-b+) can be either FYB/FYB (a true homozygoyte) or FYB/FY (an "apparent" homozygote), and you would never know, until the patient reacts with a donation that is Fy(a-b+) (true homozygote), which would be too late.  I still think that two examples of red cells is much safer, with very little extra expense.

12 hours ago, Tabbie said:

Also has anyone excluded a heterozygous anti-C negative in IAT and 1+ in enzyme (because in theory Rh should be enhanced). The panel also has an anti-D and Jkb

Yes, we do this all the time in the Reference Laboratory, although, once again, I am a little worried about so doing, but trying to find r'r', Jk(b-) red cells (even for us) is very difficult indeed, and in this case, the expense could not be justified.  In the case you give, why not just give rr, Jk(b-) blood, as if there is a proven anti-C present?

[Tabbie]

Great answers. I am also assuming that the ruling out rule is only for the panel cells not the screening cells? In that case if the example of the heterozygous anti-C negative in IAT and 1+ enzyme was the only cells you could exclude then in effect you are only able to rule out one cell ? The justification for finding r'r' Jk(b-) red cells fair enough but what if there was not an anti-Jkb ? Would you still rule out with one cell?

As there are several antibody blood group systems that display dosage not all of these are included in the guidelines 6.2.6 so why these three in particular ? Could you give the possible rationale ?

Thanks

[Malcolm Needs ☆]

Thank you for your kind comments.

What I meant to say is that r'r' red cells are so rare that I would assume an anti-C to be present, whether the r'r' red cells were Jk(b-) or Jk(b+).  I would, however, just use another example of r'r (Jk(b-) red cells, just to see how they reacted (probably would tell me absolutely nothing, but it is "belt and braces"!).  However, rr, Jk(b-) red cell donations are fairly common, whereas r'r, Jk(b-) red cell donations are much less common, and so I would avoid C+ red cell donations, which would, effectively, solve the problem (albeit, it is a bit of a fudge).

In answer to your last point, the reason that those antigens have been chosen is because the cognate antibody specificities are more common as clinically significant antibodies than are other specificities.  It is impossible to cover all bases.

[Tabbie]

1 hour ago, Malcolm Needs said:

In answer to your last point, the reason that those antigens have been chosen is because the cognate antibody specificities are more common as clinically significant antibodies than are other specificities.  It is impossible to cover all bases.

Hi Malcolm

I thought that but then what confused me is that the order of clinical significance starts with blood groups Rh (dosage occurs), KELL etc. Realise that KELL only some times exhibits dosage and that the risks of using heterozygous expression to rule out is acceptable as you have discussed in other posts.

Thanks for clarification

[Malcolm Needs ☆]

No problem - but there are reasons for this.

Although Rh antibody/antigen reactions can show dosage, it is comparatively rare for them to so do.  In addition, say we are talking about anti-C, the most common antibody specificity found with anti-C is, of course, anti-D, and so we (NHSBT) would have to provide hospitals with, not only r'r' red cells in the antibody panel, but also r'r' red cells for the screening cells - and we couldn't; they are far too rare.

The same applies to antigens within the Kell Blood Group System.  Although we (NHSBT) are able to provide an example of K+k- red cells in the antibody panel, we could not provide one in the screening cells; there are just not enough available.

In a case where a patient has already produced a clinically significant antibody, such as anti-Fy^a, BCSH Guidelines suggest that further blood transfusions should not only be Fy(a-), but also K-.  Personally, I think that we should be duty bound to ensure that the patient is not K+k-, so that they do not make an anti-k, but that is what the Guidelines say (and if the patient is K+k+, it doesn't matter anyway).

[Mabel Adams]

I allow ruling out anti-C or anti-E in the presence of anti-D using a single cell from a heterozygote for the reasons you mention plus the odds of a D negative unit being positive for those antigens are low making the risk of a missed antibody lower than in cases where we would be transfusing Rh positive blood.