I am going to be EXTREMELY controversial here, but I really don't understand why, if the cross-match is compatible, anyone would bother to type for the Cw antigen. I would be happy if someone could direct me to a RELIABLE paper that has shown anti-Cw to be clinically significant as far as an acute or delayed haemolytic transfusion reaction is concerned. I am aware of one paper in which it was claimed that anti-Cw caused hydrops in a pregnancy, but, for reasons I have given before, I do not regard this paper as reliable.
The same goes for an anti-M that is not proven to work at strictly 37oC, and many other specificities.
One only has to read the three editions of the FactsBook to see that there are numerous antibody specificities that are absolutely benign (unless your name is Lyndall Molthan - see Issitt PD. Applied Blood Group Serology. 3rd edition, 1985, Montgomery Scientific Publications, page 433. Anyone who cannot get hold of this is welcome to read my signed edition, but you'll have to give me £1 million as security, so that I get it back!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!