Confirming Antigen Negative Units from the Reference Lab

[Malcolm Needs ☆]

Slim to anorexic!

[adiescast]

I agree that typing may have been incorrect, but unless this is the case (or the donor has had a stem cell transplant), I cannot think of a situation where a donor may gain an antigen (unless you are counting something like T activation).

We (that is, the NHSBT - I am not involved personally) have been looking for the exposure of neo-antigens in blood that has passed through a prion filter and, as far as I am aware, none has been found.

I can certainly cite quite a few cases where an antigen has been weakened, even to the extent that an apparent alloantibody may be made against the antigen, but, except in the case of a Lewis antigen, such a situation only occurs, as far as I am aware, in a pathological condition. I have never heard of this happening in a healthy individual. Were it found that a healthy donor has "lost" an antigen, however, I cannot see how it is likely to be clinically significant for the recipient of that blood.

The NHSBT now garuarantees that the blood in a unit is of the ABO and D type advertised on the label (the same applies to other antigens printed on the label). In the case of a new donor, each antigen is tested twice under positive sample identification, and each antigen on the label is tested at least once on that actual donation on any regular donor.

As a result, very few of the hospitals we supply with blood now actually test the group of the unit.

At the risk of rushing in where angels fear to tread...what is the process to "guarantee" the labelled type on the unit? I know we have detected errors on units from our blood center when we retype the unit, both in ABO/Rh type and in other antigen typings. The ABO group of all units and Rh of Rh nedative units must be confirmed per AABB Standard 5.12, so it isn't an option for AABB accredited facilities to stop confirming these antigens.

[Lecia Guill]

We confirm the ABO. We do not confirm the antigen type from reference lab whether historical or actually tested. We sent it to the reference lab because we do not have the resources to do it in house. We contract with them to provide this service. Since we do the AHG crossmatch, we would catch a clerical error, if made.

Regarding the statement "Since we do the AHG crossmatch, we would catch a clerical error, if made..."

One caveat: Our transfusion service recently sent a specimen to a reference lab for antibody identification. The antibodies demonstrated 1+ reactivity and were identified by the reference laboratory as anti-Jka and anti-E. The problem is that the antibodies did not consistently react with cells HOMOZYGOUS for the Jka and E antigens.

Our thought process had been that incompatibility would always be detected at crossmatch. We have learned otherwise.

[Malcolm Needs ☆]

At the risk of rushing in where angels fear to tread...what is the process to "guarantee" the labelled type on the unit? I know we have detected errors on units from our blood center when we retype the unit, both in ABO/Rh type and in other antigen typings. The ABO group of all units and Rh of Rh nedative units must be confirmed per AABB Standard 5.12, so it isn't an option for AABB accredited facilities to stop confirming these antigens.

Hi,

The units are tested by automation from start to finish and the results MUST be downloaded automatically with no human intervention. Any groups that the automation does not recognise without human intervention means that the unit is discarded.

All units are typed twice for ABO and RhD irrespective of the number of times the donor has given.

All labels giving the groups are produced automatically and contain the unit's bar code, which is matched with the bar code on the unit before it is attached to the unit, and again afterwards.

All the bar codes are scanned to ensure that they are all the same prior to the units leaving the Blood Centre.

[Malcolm Needs ☆]

Regarding the statement "Since we do the AHG crossmatch, we would catch a clerical error, if made..."

One caveat: Our transfusion service recently sent a specimen to a reference lab for antibody identification. The antibodies demonstrated 1+ reactivity and were identified by the reference laboratory as anti-Jka and anti-E. The problem is that the antibodies did not consistently react with cells HOMOZYGOUS for the Jka and E antigens.

Our thought process had been that incompatibility would always be detected at crossmatch. We have learned otherwise.

You are completely correct Lecia; serological cross-matching WILL NOT detect all incompatible units.

There are many clinically significant atypical alloantibodies in patients (particularly Kidd antibodies) that will only react with homozygous expression of their corresponding antigen. This is why screening cells and antibody panel cells are chosen to have homozygous expression of certain antigens (and in some cases are actually checked by genotyping or flow cytometery) and are in preservative.

As I wrote in another post, this preservative is designed to preserve the antigenicity of the red cells, but not the oxygen carrying capacity.

On the other hand, units of blood are in a preservative designed to preserve the oxygen carrying capacity, but not the antigenicity.

Therefore, if you have, for example, a weak example of anti-Jka, that only reacts with red cells showing apparent homozygous expression (Jk(a+b-), and you cross-match an "elderly" unit of mis-labelled Jk(a+b+) blood serologically, it will not necessarily be incompatible.

Scares me to death sometimes!

:eek::eek:

[TimOz]

Malcolm,

I agree and I spend a lot of my time in Asia hammering this same point to labs who rely on crossmatching and cannot see the reason why they need to also antibody screen. The unfortunate thing is that so many people are not taught the importance of antigen zygosity and the 'old fashioned" concept of antibodies showing dose. I see probable failed crossmatch cases all the time when lab staff ask me "Why do my patients have so many transfusion reactions when I did a crossmatch?"

and you comment "Scares me to death sometimes!" To paraphrase Monty Python. "I got better".

[may]

Good evening ....In our lab we repeat the typing for negative antigen on donor RBC before issuing the unit to the pateint.