Microscopic examination of DAT

[bbanker2]

Is microscopic examination of a (macroscopically) negative DAT required? I think it is but I can't find where at in the Standards or Technical manual it states this. Thanks!

[clmergen]

We only perform microscopic examination on DATs for Cord Bloods. For adults, it has to be macroscopic positive for us to call it positive.

[Malcolm Needs ☆]

Is microscopic examination of a (macroscopically) negative DAT required? I think it is but I can't find where at in the Standards or Technical manual it states this. Thanks!

Peter Issitt, in at least one edition of his seminal book, "Applied Blood Group Serology" said that he thought microscopes should be banned from Blood Transfusion Laboratories.

Apart from the fact that they are required for the KBT, I agree wholeheartedly with him. They serve only to confirm very, very weak reactions, that are usually too weak to confirm (as opposed to suggest) an antibody specificity, which, at that strength is not going to be clinically significant, but as sure as h*ll delays the patient getting blood which is, to all intents and purposes, compatible.

:(:(

Edited July 28, 2010 by Malcolm Needs
as always, spellllllllling!

[L106]

Aren't you more likely to detect a transfusion reaction earlier by looking at the DIrect Antiglobulin Test microscopically for a weak mixed-field reaction?

Donna

[butlermom]

I, too, have been wondering about microscopic examinations. We use the microscope to read all DAT's, Coombs crossmatches, as well as tube antibody screens. It seems that any time we use PeG in an antibody screen, the microscopic reading looks weakly positive. Are others reading screens and Coombs crossmatches microscopically?

[Malcolm Needs ☆]

Aren't you more likely to detect a transfusion reaction earlier by looking at the DIrect Antiglobulin Test microscopically for a weak mixed-field reaction?

Donna

Yes you are, but then, if you are having to use a microscope to detect such a weakly positive DAT, are you detecting a haemolytic transfusion reaction, or a serological transfusion reaction? You would still have to go by clinical signs.

If, however, you use the gel technique for the DAT, which is much more sensitive that the tube technique, you will detect such a mixed-field reaction a lot easier, and without the use of a microscope.

:):)

Edited July 29, 2010 by Malcolm Needs
Missed a bit out.

[Steven Jeff]

I personally have not used a microscope in blood transfusion for more than 15 years - about the time when we moved totally to gel techniqes. However, even before then we used to read Antiglobulin tests by the tip and roll technique on a light box. I will admit I do not get into some of the more advanced serology that some of you do but, surely the principle is still the same.

Steve

[bbanker2]

Thanks for the feedback everybody! We only look at DATs under the microscope ...we do not read all tube screens, crossmatches, etc. (Except for Fetal Screen) I would like to eliminate it on the DATs....like Malcolm said they are too weak to confirm.

[marquij@caribe.net]

We only check microscopically the cord cell DAT's.

[Eagle Eye]

we check all our DATs microscopically. we are gel user but do not run DAT by Gel.

[David Saikin]

DAT by gel . . . love it.

[rravkin@aol.com]

Yes you are, but then, if you are having to use a microscope to detect such a weakly positive DAT, are you detecting a haemolytic transfusion reaction, or a serological transfusion reaction? You would still have to go by clinical signs.

If, however, you use the gel technique for the DAT, which is much more sensitive that the tube technique, you will detect such a mixed-field reaction a lot easier, and without the use of a microscope.

:):)

Malcolm,

What is a serologic transfusion reaction? Is it not clinically significant given the reactants involved, especially when working up a potential transfusion reaction; or is it an in-vitro induced anomally; can we tell the difference? Would it not lend to a more realistic diagnosis (for lack of better words) of the patient; and perhaps the patient's physician would want to check it again with a second specimen at a given time. You sound as if you would more readily accept a weak reaction in gel before you would accept the same weak reaction from the microscope. Do your feelings towards the use of the microscope in the blood bank revolve more around work flow as opposed to the significance of results obtained? I use the microscope sometimes in the BB and it's use can alter the workflow but only minimally for a DAT check, but much more significantly when your KHB is positive.

[KarenJ]

We also check all DAT's microscopically, but I would love to get rid of the scope. Just can't convince everybody.

[Winter]

Check the product insert for the antiglobulin reagent you are using. A relatively recent switch to Ortho AHG allowed us to forgo the microscope for reading DAT and IAT reactions.

"Resuspend the cells by gentle agitation and examine immediately for macroscopic agglutination. An optical

aid, such as a hand lens or magnifying mirror, may enhance visibility of weak reactions. "

[Yanxia]

I wonder is there someone find the elution positive and DAT neg patient , what ablut their DAT check microscopically.

I think this is a question about workflow, if we suspect hemolysis reaction we check the DAT , macroscopically, then elution we can find the binding antibodies below detect level; microscopically, maybe we can find the weak reaction , what is next , elution,too.

[Malcolm Needs ☆]

Malcolm,

What is a serologic transfusion reaction? Is it not clinically significant given the reactants involved, especially when working up a potential transfusion reaction; or is it an in-vitro induced anomally; can we tell the difference? Would it not lend to a more realistic diagnosis (for lack of better words) of the patient; and perhaps the patient's physician would want to check it again with a second specimen at a given time. You sound as if you would more readily accept a weak reaction in gel before you would accept the same weak reaction from the microscope. Do your feelings towards the use of the microscope in the blood bank revolve more around work flow as opposed to the significance of results obtained? I use the microscope sometimes in the BB and it's use can alter the workflow but only minimally for a DAT check, but much more significantly when your KHB is positive.

A serological transfusion reaction, as described by Lawrie Petz and George Garratty in "Immune Hemolytic Anemias" 2nd edition, Churchill Livingstone 2004, is a situation where, in the Laboratory, you are able to detect a positive DAT, due to a (usually) de novo antibody specificity, and, on occasions, free de novo antibody specificity within the sample's plasma, and can elute the antibody from the red cells, but, there are no clinically significant sequalae as far as the patient is concerned.

You can tell the difference from a delayed haemolytic transfusion reaction in that there is no clinically significant rise in bilirubin, no renal pathology and, even when there is a shortening of transfused red cell survival, the patient's bone marrow is able to compensate withou recourse to further transfusion.

Obviously, the physician would follow the course of such a reaction by ordering serial haemoglobins, bilirubins, etc, BUT, the physician should treat the patient; not the Laboratory results!

The use of the microscope in the Laboratory, or, should I say, my opinion of the use of the microscope in the Laboratory, is based on reading many sections in books and papers on the subject, and from experience. It is most definitely NOT based on work-flow. You will see from some of my "critics" (I use the term in its loosest sense - as a bit of fun) that I have often been accused of looking for zebras, rather than horses, when I hear the sound of hoof-beats. This, in itself, does not lead to an improved work-flow!!!!!!

I mus say, I have NEVER suggested that anyone could read a KHB without a microscope!! In fact, I said, either in this thread, or another, that this is the one reason to have a microscope in the Blood Transfusion Laboratory - although I have also argued (in the past, before reticulocytes could be determined by machines) that the KHB test is better done by a Haematologist than a Blood Banker, as they are more used to reading minor populations down a microscope, than is a Blood Banker (who rarely sees a real positive KHB).

:):)

[Likewine99]

I haven't "scoped" a DAT for over 15 years. Move to gel, way easier to read! If you're not a gel fan get rid of the scoping, the cost/benefit ratio isn't worth it.

[lalamb]

We do microscopic exams on neg Cord DAt's, and add a comment "DAT is negative microscopically"

Gives us confidence that a weak/scratchy pos isn't missed.

[rravkin@aol.com]

A serological transfusion reaction, as described by Lawrie Petz and George Garratty in "Immune Hemolytic Anemias" 2nd edition, Churchill Livingstone 2004, is a situation where, in the Laboratory, you are able to detect a positive DAT, due to a (usually) de novo antibody specificity, and, on occasions, free de novo antibody specificity within the sample's plasma, and can elute the antibody from the red cells, but, there are no clinically significant sequalae as far as the patient is concerned.

You can tell the difference from a delayed haemolytic transfusion reaction in that there is no clinically significant rise in bilirubin, no renal pathology and, even when there is a shortening of transfused red cell survival, the patient's bone marrow is able to compensate withou recourse to further transfusion.

Obviously, the physician would follow the course of such a reaction by ordering serial haemoglobins, bilirubins, etc, BUT, the physician should treat the patient; not the Laboratory results!

The use of the microscope in the Laboratory, or, should I say, my opinion of the use of the microscope in the Laboratory, is based on reading many sections in books and papers on the subject, and from experience. It is most definitely NOT based on work-flow. You will see from some of my "critics" (I use the term in its loosest sense - as a bit of fun) that I have often been accused of looking for zebras, rather than horses, when I hear the sound of hoof-beats. This, in itself, does not lead to an improved work-flow!!!!!!

I mus say, I have NEVER suggested that anyone could read a KHB without a microscope!! In fact, I said, either in this thread, or another, that this is the one reason to have a microscope in the Blood Transfusion Laboratory - although I have also argued (in the past, before reticulocytes could be determined by machines) that the KHB test is better done by a Haematologist than a Blood Banker, as they are more used to reading minor populations down a microscope, than is a Blood Banker (who rarely sees a real positive KHB).

:):)

Hey Malcolm,

Thank you for clearing that up, and for the reference, and the info, and mostly for your positive influence. It is all greatly appreciated.:) But I have to ask, how can finding an antibody bound to red cells NOT be clinically significant with respect to the patient? This is what I am understanding from the first paragraph of your post.

Edited August 3, 2010 by rravkin@aol.com

[Malcolm Needs ☆]

Thank you for your kind comments; they are much appreciated.

Well, there are plenty of examples I could give of antibodies attached to red cells that are not clinically significant in terms of compromising the patient.

Within the Rh BGS, for example, we give Cross-match compatible blood to patients with anti-Cw, rather than blood tested and found to be Cw-, without unfortunate consequences.

The same applies with anti-Kpa within the Kell BGS. The recent example of a transfusion reaction caused by anti-Kpa, published in Immunohematology, it should be noted, involved a fairly high-titre anti-Kpa that was given Kp(a+) blood by electronic issue, rather than after a serological cross-match.

Perhaps one of the more surprising examples is anti-U. Given that the first example described caused fatal HDN, and the second a fatal transfusion reaction, one would be forgiven for thinking that all examples of anti-U are cllinically significant. This, however, is not so. I know of cases where U+ blood has been transfused, in quite large amounts, to a U- patient with anti-U (in the particular one I am thinking of, it was for trauma, but only about 6 units were given, so it is unlikely that the reaction all happened on the ER or OR floor, and, in any case, there was no exchange given after the bleeding was stopped, so there were still U+ red cells, in abundance, in the circulation).

It is quite possible, although we don't know yet (we are doing a study) that this may be because the antibody was mostly IgG2 (and/or IgG4), rather than IgG1 and/or IgG3.

As you can see from these few examples, however, not all bound antibody is detrimental to the red cell to which it is bound.

:):)

[Eoin]

My Vote - Yes to Gel (or more correctly column agglutination technique - because it is not strictly a gel {you can tell we were picked up at regulatory audit for that recently :mad: and had to change the wording in our scope of practice - but we still call it gel in the lab}), No to Manual with microscopy for DAT.

Cheers

Eoin:cool: