DAT testing

[LaraT23]

We send off all Pos DAT's, our reference lab deals with checking that out. We only report pos/neg for poly, and then a room temp incubation and then check cells. If I am not mistaken ( please correct me) it is not necessary to QC your polyspecific AHG with complement cells if you are not reporting the complement portion separately as pos/neg. At least I cannot find that in any manuals. The highest signficance for bbk for positive DAT is to find an IgG component. This would be either an auto ab that shows specificity ie- rh abs, or for investigation of tranfusion. According to the AABB manual only 10-20% of persons with AIHA will have C3 as the only source of a pos DAT. In that case, a pos C3 only on a DAT is the least of their worries!

[AMcCord]

The note for TRM.40210 says "Complement-coated red blood cells should be used to confirm all negative antiglobulin tests when the antiglobulin reagent used for testing has anti-C3 reactivity." Poly has anti-C3 reactivity.

If you are doing DAT screens and you report a negative poly, is it negative because there is no IgG and/or C3 on your patient red cells? Or is it negative because your poly AHG failed to detect the C3 on the patient red cells because it has lost some of its reactivity? Without using C3 coated red cells, you can't answer that question. If you have a false negative DAT, it won't be sent to the reference lab.

It is true that a majority of WAIHA cases are due to IgG. Don't forget, however, that there are cases of severe AIHA due to C3 and they are not rare - think cephalosporin induced. The cephalsporin family is a commonly prescribed antibiotic. Even though we are a smaller facility, we have seen several cases like this, 2 extremely severe. The presence of C3 on the patient's cells and a medication history gave the presumptive diagnosis. We have also seen several very severe cases of idiopathic WAIHA due to C3. Leukemia and lymphoma patients with C3 coated cells have a worse prognosis than those patients with IgG coated cells. Treatments are modified based on what is reported. The treatment for cold agglutinin disease is affected by whether or not we report a positive DAT w/ C3. So, it can be crucial, even if not as common.

Email or phone CAP with this question. Their technical people are very helpful and respond quickly.

[LaraT23]

I was thinking of implementing DAT done in the gel. That has an IgG component only and offering a separate DAT for AHG. Although I am not sure how to incoporate ordering. Of course any DAT's done for transfusion reactions would have to be AHG but I simply cannot keep complement coated red cells for QC. Did someone say they knew of a way to make them???

[LaraT23]

I just noticed that the question you quoted has a commentary that reads " If polyspecific antiglobulin is used, refer to question TRM.40200". That one reads, are IgG -coated red cells used for poly , and they are. So that answers that!

[mhc]

I just noticed that the question you quoted has a commentary that reads " If polyspecific antiglobulin is used, refer to question TRM.40200". That one reads, are IgG -coated red cells used for poly , and they are. So that answers that!

Phew! I was trying to figure out how to use both the IgG and C3 coated cells for one poly DAT test!

[AMcCord]

Look closer at TRM.40200. It says IgG coated cells must be used for testing that has 'anti-IgG reactivity', which poly does (and so does anti-IgG). TRM.40210 says complement-coated red blood cells should be used to confirm all negative results when testing has 'anti-C-3 reactivity, which poly also does.

Set up 2 tubes with poly AHG. The first tube is read at immediate spin for IgG reactivity with negatives checked with IgG coated cells. The second tube can be read at immediate spin, but it is recommended to incubate at RT for 5 minutes to increase sensitivity for C-3 activity. If the second tube is negative (no C-3 reactivity), control it with complement coated cells. Both IgG and C-3 reactivity are covered for your patient and QC is done for both types of reactivity.

[mhc]

I suppose that is what CAP is requiring, although I've always looked at coombs control cells as an assurance that the AHG reagent was actually added to the test, not as a "positive control".

Tell me, do/would you set up all tests that use poly AHG in duplicate (panels, screens etc.)?

[AMcCord]

What we preach to MT/MLT students about control cells (either IgG or complement coated) is that it's all about... did we add it, did we wash it (and we aren't neutralizing our AHG by not washing well enough), and did it work.

Complement control cells are a part of the QC for DATs. There is no requirement to detect C3 activity for screens, IDs or AHG crossmatches and our life is easier if we avoid finding it there . I hate cold agglutinins! There could be a rare case where it become important, but I haven't seen one of those yet (did I just jinx myself?).