What is the most likely antibody if a patient's plasma tested positive with all cells but negative after treatment with EDTA/glycine acid?

The presence of an antibody that reacts positively with all cells but shows a negative result after treatment with EDTA/glycine acid indicates that it is likely to be a low-incidence antibody. This treatment is designed to remove certain types of antibodies through a method known as competitive inhibition, which is effective against certain antigen-antibody interactions.

The antibody associated with the Kpb antigen, which is of low incidence, matches this scenario. Anti-Kpb can cause a positive reaction with a broad panel of cells if those cells carry the corresponding antigens, and its reactivity can be diminished after treatment with EDTA/glycine acid, due to the alteration of the protein structure of the red blood cells involved in the antibody binding.

In contrast, Anti-Fy3, Anti-Jk3, and Anti-Rh6 are either more common or are known to behave differently under such treatments, thus would not lead to the same pattern of reactivity as seen here. The selective reactivity with all cells and subsequent loss of reactivity post-treatment aligns well with the characteristics of Anti-Kpb, making it the most likely antibody in this context.