Antigen typing on a patient with a positive DAT?

[sniedz]

Our protocol for antigen typing patients is they can't have had a transfusion within the past 3 months and their DAT has to be negative. I went to a Blood Bank seminar a few weks ago and the case study presented had a positive DAT, but no recent transfusions. They antigen typed him. When I questioned this (because of his positive DAT), they said they use monoclonal direct antisera and you can type on patient's with a positive DAT. Does anyone use this practice?

[JOANBALONE]

Yes. Review your manufacturer's instructions for use and run proper controls. Antisera that use the IAT method would not be a good choice if your patient has a positive DAT.

[Malcolm Needs ☆]

Yes. Review your manufacturer's instructions for use and run proper controls. Antisera that use the IAT method would not be a good choice if your patient has a positive DAT.

I agree entirely with you JOANBALONE, but would add that, even if the DAT is positive, and you only have IAT grouping reagents available, with suitable controls, and with a knowledge of what antigens are degraded by the substance, you can treat the patient's red cells with chloroquine diphosphate to remove the antibody causing the positive DAT, and then test the red cells.

The method can be found in, amongst other publications, The AABB Technical Manual (16th edition) on pages 894 and 895.

:D:D:D:D

[ckcheng]

(1) One has no transfusion within the past three months does not mean he/she is DAT negative. So a negative control in typing is important especially when you are using IAT technique.

(2) Monoclonal antisera, like anti-E, -e, -C, -c, -Jka, -Jkb, -S, etc, has the advantage of that you can type patient whose red cells are DAT positive cuz only direct agglutination step, no IAT is required.

(3) agree that follow manufacturer's instruction is important.

By the way - hi Malcolm, you bought a copy of Technical Manual ?!

CK Cheng, MSc, SBB(ASCP), CQA(ASQ)

Oct 5, 2010

[Malcolm Needs ☆]

(1) One has no transfusion within the past three months does not mean he/she is DAT negative. So a negative control in typing is important especially when you are using IAT technique.

(2) Monoclonal antisera, like anti-E, -e, -C, -c, -Jka, -Jkb, -S, etc, has the advantage of that you can type patient whose red cells are DAT positive cuz only direct agglutination step, no IAT is required.

(3) agree that follow manufacturer's instruction is important.

By the way - hi Malcolm, you bought a copy of Technical Manual ?!

CK Cheng, MSc, SBB(ASCP), CQA(ASQ)

Oct 5, 2010

Hi There,

No, I didn't. It is better than that; my employers, the National Health Service Blood and Transplant bought one for each of the Reference Laboratories - so in a sense, I got it for free!

Trouble is, of course, I have to leave it at work, rather than bring it home with me, but hey, you can't have everything in this world!!!!!!!!!!!!

I haven't forgotten your email by the way; the IBMS SAC for Transfusion Science is meeting later this week, after which I should, hopefully, be able to give you an answer.

:D:D:D:D

:D:D:D:D

Edited October 5, 2010 by Malcolm Needs
Spelling - yet again!

[ckcheng]

Hi Malcolm, sounds great cuz the Technical Manual is quite expensive. I started to buy every edition since I started my SBB program. I have three at home now, haha. There are lots nice books that you are right, you can not have everythings in the world. Take care.

Thanks.

Chun-kwok

Oct 5

[Yanxia]

I remember have heen read a paper about a DAT posittive patient use monoclonal direct antisera but because the antibodies bond on the red cells block the antigens ,so the result is a false negative.

Malcolm, if in this kind of situation, what can we do, just elution? And if this happen , I think lots of us will not concious this is the blockage.

[Malcolm Needs ☆]

This situation has been recorded, but it is very, very rare; but, yes, elution would show what antibody is sensitising the red cells.

I should warn you to be very careful with this - occasionally, you can elute an antibody specificity that is mimicking. We have a patient from whose red cells we have been able to elute an apparent anti-K for years and years, but he is plainly K-, and has never been transfused with K+ red cells or components.