For UK members here worried about jw admin staff getting a look at any letter you might write contradicting the blood card you can ask to do what I did. Have the letter put on EKIS in a secret folder that is not open to mere admin staff but only to DR's. This way if there is a jw receptionist for instance, she won't have access to the letter. And if an alert is put on saying in the event of blood being needed to check out the letter in the secret file, well she would have no idea what the letter says and would probably assume it's a copy of the blood card.
That's how it works in the UK at least, I don't know about other countries.