Labels are used to help us describe and understand the world around us. Calling glass "sand" isn't helpful, because glass and sand have vastly different properties and are used very differently. Calling a MtF trans-person a woman can have some advantages for some people. For example in a sexual context, they may be perceived by their partner as a woman, and that may be enough to get them off. But using the same label in a medical context would probably make less sense, because it's still a male. Albeit maybe with less testosterone, breast implants, plastic surgery or castration. But I'm sure a medical doctor will still take these factors into consideration, even though they may not see the patient as a biological female in order to not misdiagnose and hurt the patient.