How could one titrate an allo-antibody in a pregnant woman who also has an autoantibody (even if the auto is weak, reacting only w+ in saline AHG against cells negative for the antigen to which the allo-antibody is directed & DAT 1+, IgG only)?  Trust me that the allo is really an allo. The DAT was due to a warm auto not a transfusion or FMH.  Is a meaningful titer possible in this situation?

Could you not do an auto-adsoption on the mother's plasma and then titrate with the adsorbed plasma?

_{I agree with Anna.} 

If your auto-antibody is that weak (weak results only with red cells not expressing the antigen against which the antibody is directed), then I would think that the titre that you get with red cells that do express the antigen against which the antibody is directed would be fairly accurate, with not much in the way of boosting by the auto-antibody.

 

The problem with performing an alloadsorption first, to get rid of the autoantibody (and, because the patient is pregnant, an autoadsorption is out of the question), prior to performing the titre, is that, however careful you are getting the alloadsorption red cells as packed as possible, you will get some dilution due to the medium in which the alloadsorption red cells are suspended.

 

So, to a certain extent, you pays your money and you takes your choice as to whether you want a very slight boost to the titre by ignoring the very weak auto-antibody, or you want a very slight dilution after alloadsorption, bringing down the titre very slightly.

I had assumed that adsorptions would introduce dilution.

 

The patient was tested at a reference lab in December and the warm auto was found (1+ DAT) along with an anti-e (she is R2R2).  At that time it had been more than 3 months since she was pregnant and transfused (yes, both).  They followed Malcolm's logic and did a titer of the anti-e using unaltered plasma, which was 64.  Now the warm auto is undetectable (DAT negative) but we find an anti-e, anti-C and anti-S in gel. The titer of the anti-e & C against S negative, R1R1 cells is now 8.  The reference lab did not let us know if the titer cell they used was S+ or not. I assume it was C pos.  We do our titrations by the same method as the reference lab--saline 60 min AHG.  The anti-S titer is <1 (reacts in gel but not in saline AHG with neat plasma).  I am trying to figure out which of several variables could have made her titer drop by that much.  She is now 2nd trimester.  Even if we add the effect of the autoantibody plus using S+ cells, would we get that much difference in the titer? What other factors could contribute?

I, personally, think that the change in titre from 64 down to 8 is fairly normal; I've seen this kind of things many times, although I have seen the opposite (titre going from 8 to 64) much, much more frequently.

I, personally, think that the change in titre from 64 down to 8 is fairly normal; I've seen this kind of things many times, although I have seen the opposite (titre going from 8 to 64) much, much more frequently.

Do you mean it is fairly normal in the context of a warm autoantibody with the allo or in more typical titer cases?

Hi Mabel,

I have seen it much more often in the case of an auto-antibody (as these are cases where the patient is being treated with immunosuppressive drugs), but I have, nevertheless, seen it in cases of an alloantibody - but I couldn't tell you why the titre should fall!

We've recently had a case where we followed an anti-G+C throughout a pregnancy, and the titre decreased as the pregnancy went on. Of course, we have also seen cases of anti-Tca when the same thing has happened, but that would be expected, as this specificity is adsorbed onto the surface of the placenta.