This blood group system, formerly known as “Cartwright,” is actually built on an enzyme called acetylcholinesterase (AChE). The enzyme is responsible, in other parts of the body, for deactivating acetylcholine and stopping a nerve signal, but we aren’t sure with AChE does on an RBC.
The structure carries two antigens, the very high-prevalence Yta (present in over 99.8% of most populations, according to “The Blood Group Antigen FactsBook,” 3rd ed.) and the much less frequently seen Ytb. Most of the issues we see in this system are with the rare Yta-negative person who forms anti-Yta. This is a troubling antibody, because it is usually benign, but it has occasionally caused hemolytic transfusion reactions. Every anti-Yta acts differently, so each must be evaluated for possible hemolytic potential (such testing may include a “monocyte monolayer assay“).
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