Daniel,
My guess is that you are used to a more liberal organization that most of us being in Switzerland. They may simply try to reason with you and that would be the end of it. if they ask you the "loyalty questions" as JWfacts brought out, do not answer yes or no. Give them another answer. Something like, "well I certainly believe the slave tries their best but they are imperfect as well". Something that deflects, and doesn't make you lie (unless you don't care about that i guess).
In addition, have your arsenal ready just in case. Reason with them from the sciptures. 3 of my favorite points are below.
1) White blood cells are forbidden but make up less than 1% of blood volume. Ambumin (a protein) makes up more than double that, but is allowed. Who decided this? What is the principle it is based on? In the medical community those are both "fractions" of whole blood.
2) Jesus told the Pharisees that David was justified in eating the showbread, because life was at stake. How does Jehovah feel about children with sickle cell anemia or trauma situations where nothing but whole blood will do? What was the point of "mercy not sacrifice" in Jesus words.
3) The prohibition was on eating blood specifically. If you are bleeding out, you cannot drink blood and live. if you are starving, you cannot put food in your veins, you need a feeding tube. Could ones conscience decide that a blood transfusion is using the blood for its intended purpose?
Bonus: The Noachian creed was a dietary restriction, and the animals were bleed because they were dead. Well you are not getting blood from dead donors. They are very much alive! In the case of organ transplants which are a "conscience matter" the donor is usually dead.
Record it! You don't have to share it unless you want to. maybe just a transcript. This is the best weapon we have right now.
Also, be respectful. DOn't get into a mess. Your wife will see you went, and that is that. If she thinks you were hard headed more than they just didn't have the answers, it could make that difficult.