Extent of ID of antibodies to Low Freq antigen

[Mabel Adams]

At my prior workplace, our blood supplier had only the few commercially available antisera to low-frequency antigens so there was not much point in sending low freqs for ID since the only option was going to be XM compatible units regardless of the ID. Now, I have ARC as a supplier and they have much more access to unusual antisera. What do others do--send all low freqs out for ID, send selected samples (likely to need frequent transfusion or with other antibodies requiring that screened units be sent in), or just give XM compatible units? I want to do cost-effective but good medicine.

[Malcolm Needs ☆]

At my prior workplace, our blood supplier had only the few commercially available antisera to low-frequency antigens so there was not much point in sending low freqs for ID since the only option was going to be XM compatible units regardless of the ID. Now, I have ARC as a supplier and they have much more access to unusual antisera. What do others do--send all low freqs out for ID, send selected samples (likely to need frequent transfusion or with other antibodies requiring that screened units be sent in), or just give XM compatible units? I want to do cost-effective but good medicine.

As a Reference Service Manager (and not yet totally driven insane; despite what Rashmi may say) I would thoroughly recommend not bothering to send in your samples from patients with antibodies directed against low-frequency antigens, and just give cross-match compatible blood!

For one thing, identifying the specificity of such an antibody (if it's not something like an anti-Wra) is like looking for a needle in a haystack.

For another, such a patient usually makes multiple specificities of antibodies directed against low-frequency antigens, and so a) we would probably never identify all those present, as we do not have access to red cells expressing every low-incidence antigen, and very often, a cell that has been identified as, for example, Li(a+) isn't, because it was identified with an anti-Lia that also had, for example, anti-Bxa in it, but we didn't know that.

Lastly, for now (as my rant muscle is running on low) the chances of you cross-matching blood, and then giving a unit that is likely to cause a clinically significant haemolytic transfusion reaction are so low as to be all but zero (just think of the number of patients who have been given blood by electronic issue, some of whom must have antibodies directed against low-incidence antigens, and some of whom have probably been given blood positive for the corresponding low-incidence antigen, and you see what I mean).

I shall now go and lie down in a darkened room!!!!!!!!!!!!!

:crazy::crazy:

[clmergen]

We don't bother with identifying antibodies to low incidence antigens. We do a Deviation Report that our Medical Director signs.

[Maximiliano]

Hi,

Do you think that the increasing availability of affordable genotyping techniques that allow the unequivocally identify many low-frequency antigens will change the way these cases (the ones presented in this post) are managed in the near future?

I'm keen to read your opinions. Thanks in advance.

Regards,

MAXI

[Malcolm Needs ☆]

Hi,

Do you think that the increasing availability of affordable genotyping techniques that allow the unequivocally identify many low-frequency antigens will change the way these cases (the ones presented in this post) are managed in the near future?

I'm keen to read your opinions. Thanks in advance.

Regards,

MAXI

Eventually yes, without doubt; but not yet.

It may be more affordable, but it is not yet cheap, and it is the primers that are expensive.

[adiescast]

I agree with Malcolm (both posts, actually). It is not worth the time and expense to try to fully chase down antibodies to low frequency antigens. Once you've done it, you can't even be sure that you are right, because they have not all been identified AND there tends to be more than one on any particular cell. Unless, of course, you want to follow up with some significant research and get one named after you!

:cool:

[Malcolm Needs ☆]

Eventually yes, without doubt; but not yet.

It may be more affordable, but it is not yet cheap, and it is the primers that are expensive.

This answer was written in haste (I had to go and get my son from his Kids' Club!) and is now being somewhat repented at leisure!

As I intimated in an earlier post above, the frequency of atypical alloantibodies directed against low-frequency antigens is far higher than the frequency of such antigens themselves. As a result, when one encounters such an antibody, it is very easy to provide antigen negative blood.

One has to ask, therefore, is the cost of the primers (which are expensive) in such a situation justifiable, for such a small return (which, if one leaves out the esoteric science of furthering man's knowledge, is virtually nil).

I can really only see one situation in which such expense could be justified.

This would be in the case of a patient requiring life-saving (but not urgent) surgery, who has an atypical alloantibody directed against a high-frequency antigen (for example, anti-Dib). Searching for Di(a+b-) donors by traditional serological techniques would be extremely expensive in terms of using very rare antisera (either anti-Dia or anti-Dib). To find suitable Di(a+b-) donors could be done by mass genotyping, but even then, it is more likely to be done by use of microarray technology than "traditional" genotyping (if I am justified in using the term "traditional" about a very new technology)!

I cannot see the expense being justified in other circumstances; but I could be wrong (again)!

:):)

[jcdayaz]

As a Reference Service Manager (and not yet totally driven insane; despite what Rashmi may say) I would thoroughly recommend not bothering to send in your samples from patients with antibodies directed against low-frequency antigens, and just give cross-match compatible blood!

For one thing, identifying the specificity of such an antibody (if it's not something like an anti-Wra) is like looking for a needle in a haystack.

For another, such a patient usually makes multiple specificities of antibodies directed against low-frequency antigens, and so a) we would probably never identify all those present, as we do not have access to red cells expressing every low-incidence antigen, and very often, a cell that has been identified as, for example, Li(a+) isn't, because it was identified with an anti-Lia that also had, for example, anti-Bxa in it, but we didn't know that.

Lastly, for now (as my rant muscle is running on low) the chances of you cross-matching blood, and then giving a unit that is likely to cause a clinically significant haemolytic transfusion reaction are so low as to be all but zero (just think of the number of patients who have been given blood by electronic issue, some of whom must have antibodies directed against low-incidence antigens, and some of whom have probably been given blood positive for the corresponding low-incidence antigen, and you see what I mean).

I shall now go and lie down in a darkened room!!!!!!!!!!!!!

:crazy::crazy:

haha malcolm....

I have always abided by the theory of "If you see hoof-prints...look for horses first, if you don't find horses, then pursue the zebras"...

The low-incidence things are generally "zebras" and not clinically significant. (Which you already know).

[Mabel Adams]

I have been accused of looking for unicorns when I hear hoofbeats!

We once had a patient that got blood every month. She had anti-K and anti-Kpa. After several years her anti-Kpa was no longer detectable--hence an antiglobulin xm would be useless to detect a Kpa pos unit. We ended up just hoping for the best with gel xms and she moved away before we ever gave her another Kpa pos unit.

Does everyone find this an acceptable risk also?

[jcdayaz]

I have been accused of looking for unicorns when I hear hoofbeats!

We once had a patient that got blood every month. She had anti-K and anti-Kpa. After several years her anti-Kpa was no longer detectable--hence an antiglobulin xm would be useless to detect a Kpa pos unit. We ended up just hoping for the best with gel xms and she moved away before we ever gave her another Kpa pos unit.

Does everyone find this an acceptable risk also?

In our institution we would never antigen type a potential donor unit for Kpa (of which I am aware). We would be perfectly comfortable with gel XM compatible blood. Is there a risk? Yes. Is it worth taking? In our opinion--YES!!

[Malcolm Needs ☆]

In our institution we would never antigen type a potential donor unit for Kpa (of which I am aware). We would be perfectly comfortable with gel XM compatible blood. Is there a risk? Yes. Is it worth taking? In our opinion--YES!!

I, too, would be happy with this.

[Maximiliano]

Thank you every body for your comments. It's been very interesting to follow this thread.

[AndyMiller]

At my prior workplace, our blood supplier had only the few commercially available antisera to low-frequency antigens so there was not much point in sending low freqs for ID since the only option was going to be XM compatible units regardless of the ID. Now, I have ARC as a supplier and they have much more access to unusual antisera. What do others do--send all low freqs out for ID, send selected samples (likely to need frequent transfusion or with other antibodies requiring that screened units be sent in), or just give XM compatible units? I want to do cost-effective but good medicine.

Hi Mabel

i find that students on courses insist on identifying everything - I often ask where the cut-off is between treating the sample as an academic exercise and actually doing stuff which will help the patient. Also better to have a patient having a transfusion reaction than perfect serology and a corpse. This is so much easier said than done though - by our very nature we want to explain why we are getting the reactions we are seeing.

I wonder how many antibodies to private antigens are missed each year because they are not present on screening cells and panel cells? My money is on, "quite a lot" and it doesn't seem to present many problems.

From my time in a Reference Lab I can do nothing but agree with Malcolm about what a pain they are to do - tube after tube of no agglutination!

Andy

[Mabel Adams]

We can't really identify anti-Colton b with our current panels. It is positive in 7-8% of donors. Does everyone consider this a "low frequency antigen" also?

Some areas have populations with higher levels of Dia antigen (S Amer Indians and Asians have higher levels than Caucasians). If your donor population has 10 or 20% of an antigen, at what level do we no longer consider it low-frequency?

[Malcolm Needs ☆]

We can't really identify anti-Colton b with our current panels. It is positive in 7-8% of donors. Does everyone consider this a "low frequency antigen" also?

Some areas have populations with higher levels of Dia antigen (S Amer Indians and Asians have higher levels than Caucasians). If your donor population has 10 or 20% of an antigen, at what level do we no longer consider it low-frequency?

I agree with you Mabel that one has to identify "low incidence" antigens in your particular area of the world (and, come to that, amongst your own ethnic minorities now that we have a "global village") that are not "low incidence" in your own area (Cw in Latvia, Di(a), as you say in South America and parts of Asia, Mi(a) in parts of Asia, etc) and treat those differently to true low incidence antigens. I would suggest that the ISBT definition of <1% in one's own ethnic admix is a starting place.

Incidentally, we would identify an anti-Cob with our panels (in the Reference Laboratory), but only if the antibody has been detected by the referring establishment in the screen/antibody panel in the first place.

:)

[Steven Jeff]

We picked up an Anti-Cob earler this year in my small laboratory as the antigen just happened to be on one of the screening cells (3 cell screen). In our lab we only have access to a 10 cell panel which also had one Cob postive cell. Fortunately the new identification panel had just arrived with 2 Cob postive cells. I remember discussing this with one of Malcom's staff who reassured me on my interpretation - you must remember I don't consider myself an expert and will always ask someone with more knowledge than myself. We sent a sample to the reference lab who duly confirmed the Anti-Cob.

As Malcolm says it depends on whether the screening cells have a Cob positive antigen on them whether we pick them up.

Steve

:)

[Mabel Adams]

Since my panels seldom have Cob pos cells labeled, although they may well be present, I have no good way of knowing whether the extra reaction I have detected (probably in a patient with anti-K or E since our screening cells are unlikely to have the antigen) is due to anti-Cob or anti-Ina unless I send it out to be identified.

Maybe I just need to switch panel cell companies.

At 2% Kpa doesn't qualify as low frequency by the 1% rule.

[Malcolm Needs ☆]

Since my panels seldom have Cob pos cells labeled, although they may well be present, I have no good way of knowing whether the extra reaction I have detected (probably in a patient with anti-K or E since our screening cells are unlikely to have the antigen) is due to anti-Cob or anti-Ina unless I send it out to be identified.

Maybe I just need to switch panel cell companies.

At 2% Kpa doesn't qualify as low frequency by the 1% rule.

I'm not certain that detecting an anti-Cob matters too much anyway, to be honest. We always tell our Hospitals to give cross-match compatible blood in such a situation, and this has never resulted in a clinically-significant haemolytic transfusion reaction.

The other thing that points in the direction of anti-Cob being not too much of a clinical problem is that there MUST have been patients with an unrecognised anti-Cob in their plasma, who have received Co(a+b+), and, possibly, although it is rare, Co(a-b+) blood through electronic issue, and I have not seen a report of a clinically-significant haemolytic transfusion reaction through this route due to anti-Cob.

I agree with you Mabel that, within the White population, a 2% frequency for Kp(a) does mean that it is not counted as low-frequency, but a frequency of 0.01% in the Black population means that it does. As I said above, one has to look at the admix of the ethnicity of the population with whom you are dealing.

:):)

[Mabel Adams]

So now I have a prenatal specimen that has a reaction of 1+ in gel with one of 2 screen cells but a neg panel and a neg PEG 3 cell screen (different screen cells, of course). Second pregnancy for the patient; no known problems with first baby. This screen cell lot was opened the day of this testing and this cell has not reacted unexpectedly on any other patient. Do we turn it out as neg because the PEG screen was neg? Try to repeat the testing on a new specimen before these screen cells expire? Send it out for ID now or if the new specimen still reacts? Test the Mom's sample against the purported father's cells (assuming he's ABO compatible which is reasonably possible since Mom is A)? Not worry about it since it is pretty weak and even if it is an antibody to a low-freq Ag, the dad will surely be heterozygous so this baby may be fine. Of course, I have seen antibodies develop during a single pregnancy that required intervention by time of delivery. This mom won't be routinely tested again this pregnancy since she is A+. And just because it is weak and we don't know what it is, we can't be sure it is clinically insignificant without IDing it.

Would your answer be any different if this mom were your daughter or if you were the pregnant woman (stretch a bit here Malcolm)? What about if you were the hospital's risk manager?

Just trying to sight-in my zebra/unicorn scope.

[Malcolm Needs ☆]

So now I have a prenatal specimen that has a reaction of 1+ in gel with one of 2 screen cells but a neg panel and a neg PEG 3 cell screen (different screen cells, of course). Second pregnancy for the patient; no known problems with first baby. This screen cell lot was opened the day of this testing and this cell has not reacted unexpectedly on any other patient. Do we turn it out as neg because the PEG screen was neg? Try to repeat the testing on a new specimen before these screen cells expire? Send it out for ID now or if the new specimen still reacts? Test the Mom's sample against the purported father's cells (assuming he's ABO compatible which is reasonably possible since Mom is A)? Not worry about it since it is pretty weak and even if it is an antibody to a low-freq Ag, the dad will surely be heterozygous so this baby may be fine. Of course, I have seen antibodies develop during a single pregnancy that required intervention by time of delivery. This mom won't be routinely tested again this pregnancy since she is A+. And just because it is weak and we don't know what it is, we can't be sure it is clinically insignificant without IDing it.

Would your answer be any different if this mom were your daughter or if you were the pregnant woman (stretch a bit here Malcolm)? What about if you were the hospital's risk manager?

Just trying to sight-in my zebra/unicorn scope.

Don't know what you mean Mabel:sarcasm:!!!!!!!!!!!!!!

I would go with testing the father against the mother's plasma/serum first. Even if the mother and father are ABO incompatible, you could always use blood group substance to take out the mother's ABO antibodies or, better still, as this may dilute out such a weak antibody, adsorb the mother's antibody onto the screening cell, and then elute it. This will leave the putative low-incidence antibody free of maternal ABO antibodies.

If then the father's red cells react against the isolated antibody, then I would pull out all the plugs to identify the specificity. As you say, this antibody could have been formed in the previous pregnancy (or in this pregnancy) and could get stronger (and more clinically significant) during the pregnancy.

Identification of any such antibody is a pain, but identification may help predict if it has the potential to cause haemolytic disease It could be one that is known to adsorb onto the apical surface of the placenta, such as an antibody in the Cromer Blood Group System, in which case there should be no more worries, but it could equally be one that has been known to cause problems in the past.

If dad doesn't react with the isolated antibody, then, hey, life's a dream and I wouldn't take it any further.

I'm always more worried about potential HDNF in these cases than transfusion.

Hope this helps (even if I'm not pregnant myself)!!!!!!!!!!!!!!!!!

:D:D:D:D

[Malcolm Needs ☆]

I've just thought, the other thing you could try is to treat the "offending" screening cell with chloroquine diphosphate, just in case it has a strong Bg antigen and the mum has made HLA antibodies (quite possible in pregnancy).

[mollyredone]

Wow, this is an old thread, but I've found it very interesting:)

[Byfaith]

As a Reference Service Manager (and not yet totally driven insane; despite what Rashmi may say) I would thoroughly recommend not bothering to send in your samples from patients with antibodies directed against low-frequency antigens, and just give cross-match compatible blood!

For one thing, identifying the specificity of such an antibody (if it's not something like an anti-Wra) is like looking for a needle in a haystack.

For another, such a patient usually makes multiple specificities of antibodies directed against low-frequency antigens, and so a) we would probably never identify all those present, as we do not have access to red cells expressing every low-incidence antigen, and very often, a cell that has been identified as, for example, Li(a+) isn't, because it was identified with an anti-Lia that also had, for example, anti-Bxa in it, but we didn't know that.

Lastly, for now (as my rant muscle is running on low) the chances of you cross-matching blood, and then giving a unit that is likely to cause a clinically significant haemolytic transfusion reaction are so low as to be all but zero (just think of the number of patients who have been given blood by electronic issue, some of whom must have antibodies directed against low-incidence antigens, and some of whom have probably been given blood positive for the corresponding low-incidence antigen, and you see what I mean).

I shall now go and lie down in a darkened room!!!!!!!!!!!!!

:crazy::crazy:

Just curious about the Anti-Wra remark. We have a patient whom our reference lab identified an Anti-Wra (among other things - sample was sent for Allo-absorption ; Warm Auto and Anti-E present). Currently we have one panel cell that is Wra+ and can show the antibody to be demonstrable in room temp. phase, so fairly comfortable to issue E Neg units compatible by Liss-AHG and RT crossmatches. The Anti-Wra is only about 1-2+ in RT phase, so wondering where we will stand if A. titer decreases or even more likely B. we don't have a Wra pos panel cell to determine if currently reactive.

We probably would have remained blissfully ignorant had our reference lab not worked this sample up for other issues! Sounds like it can be clinically significant??

[Malcolm Needs ☆]

Just curious about the Anti-Wra remark. We have a patient whom our reference lab identified an Anti-Wra (among other things - sample was sent for Allo-absorption ; Warm Auto and Anti-E present). Currently we have one panel cell that is Wra+ and can show the antibody to be demonstrable in room temp. phase, so fairly comfortable to issue E Neg units compatible by Liss-AHG and RT crossmatches. The Anti-Wra is only about 1-2+ in RT phase, so wondering where we will stand if A. titer decreases or even more likely B. we don't have a Wra pos panel cell to determine if currently reactive.

We probably would have remained blissfully ignorant had our reference lab not worked this sample up for other issues! Sounds like it can be clinically significant??

Hi Byfaith,

I could not agree with you more that anti-Wra can, on occasions, be extremely clinically significant, having caused both severe HDN and severe transfusion reactions, but this is in cases where the antibody was of relatively high titre, but was "missed" during the pregnancy and during cross-matching. Such cases are, however, very few and far between in the literature (and, in all cases, as far as I know, involved an anti-Wra that reacted well by IAT at 37oC).

In terms of a transfusion problem, however, although anti-Wra is found in about 1 in 100 or more random serum samples, and more commonly in post-partum women, the chances of such an individual being transfused with a unit of Wr(a+) blood is very low. Studies have shown that the percentage of Wr(a+) individuals within several populations ranges from 0% to 0.0011% (see the figures on page 357 of Geoff Daniels' book Human Blood Groups, 2nd ed, 2002, Blackwell Scientific).

Therefore, should your patient's anti-Wra "disappear", then it is most unlikely to be clinically significant or to cause a HTR. On the other hand, if you have no Wr(a+) red cells available, but the anti-Wra strengthens to become reactive by IAT, as long as blood is cross-matched for your patient, then there should be no problems with transfusions - you just don't give a unit that is incompatible.

As you say yourself though, in a sense, ignorance is bliss. Antibodies directed against low incidence antigens are actually quite common ( we once had a cell in the panel that was Lu:6, and we found numerous examples of anti-Lu6 - which was a nuisance, but no more than a nuisance), but we just never detect them (unless we are purposely looking for them), because we do not have red cells available that express the corresponding antigen - but these antibodies rarely, if ever, cause any real problems. As I say, if they did, we would not be able to perform electronic issue, but this is now commonplace, and there are no floods of reports of transfusion reactions due to such antibodies.

I hope that all this waffle has helped to allay any fears you have. If not, I'll have another go - you have been warned!!!!!!!!!!!

[Tabbie]

Great reading ....good point with electronic issue thanks