An update on the Cartwright (Yt) blood group system.

This update of the Cartwright blood group system (George MR. Cartwright blood group system review. Immunohematology 2012;28:49-54) reports the addition of three new antigens. From 1956 until 2017, the Cartwright (Yt) blood group system consisted of two antigens, Yta and Ytb. Yta is a high-prevalence antigen, and its antithetical antigen, Ytb, shows much lower prevalence. In 2017, YTEG was identified, and, in 2018, the International Society of Blood Transfusion added high-prevalence antigens YTLI and YTOT. Cartwright antigens result from point mutations in the acetylcholinesterase gene on chromosome 7q. Little is known about antibodies against YTEG, YTLI, and YTOT. Discovery of these new antigens required plasma inhibition studies and molecular analysis for further characterization. Based on experience with Yta and Ytb, Cartwright antibodies have rarely demonstrated clinical significance; nevertheless, cases of in vivo hemolysis have been reported, suggesting that clinical significance should be interpreted on a case-by-case basis.