Could this cause false negative DAT?

[Clarest]

If patient's red cells are heavily coated with antibody (e.g., cord blood cells coated by maternal antibody(ies) with high titer), is it possible to cause a false negative DAT result?

Thank you!

 

 

[Malcolm Needs ☆]

Most certainly it can.

There have been published papers on newborn babies being typed as D Negative, and K Negative, not because they have received an IUT, but because their mother's antibody has such a high titre that they sensitise virtually every antigen site on the cord red cells, thus causing a sort of prozone effect.

The same can happen with a "blocking antibody" and AHG.

It is also not uncommon for newborn babies with ABO HDFN to have a negative DAT, and be released from hospital, only to be brought in again when they become "floppy", and for the DAT to then be positive.

[Clarest]

Hi Malcolm,

Thank you for your response. I kind of understand the theory for every antigen site being occupied by the maternal antibody, so nothing available for binding the antibody in the antiserum. However, for DAT, we add the anti-IgG to bind the antibody. Is the antibody still available to react with anti-IgG? I was thinking if the false negative result is caused by insufficient wash by normal wash cycles?

In addition, I just usually consider the interference of positive DAT to indirect testing but have never thought that could interfere with direct agglutination testing, such as ABO, RhD, K phenotyping. 

 

[Arno]

This phenomenon is also described with the monoclonal antibody therapy anti-CD47 (Hu5F9-G4) where red cells are so heavily loaded with IgG that it creates steric hindrance. Basically, antibodies bound to the red cells hinder the binding sites of the anti-human globulin leading from very weak to negative DAT. Anti-CD47 can be eluted off the red cells and it gives very strong reaction in IAT. Of note: it is not the same mechanism involved with the anti-CD38 (another monoclonal antibody therapy often called DARA) where here the DAT can be negative too because of down-regulation of CD38 expression onto the red cell membrane.         

[Clarest]

On 7/12/2022 at 8:28 AM, Arno said:

This phenomenon is also described with the monoclonal antibody therapy anti-CD47 (Hu5F9-G4) where red cells are so heavily loaded with IgG that it creates steric hindrance. Basically, antibodies bound to the red cells hinder the binding sites of the anti-human globulin leading from very weak to negative DAT. Anti-CD47 can be eluted off the red cells and it gives very strong reaction in IAT. Of note: it is not the same mechanism involved with the anti-CD38 (another monoclonal antibody therapy often called DARA) where here the DAT can be negative too because of down-regulation of CD38 expression onto the red cell membrane.         

Hi Arno,

Thank you for the explanation! Actually I had a sample from a patient on DARA yesterday showed 1-2+ positivity with all screening and panel cells, but DAT was negative.